US 4812820

I'll verify this patent number against live sources and check for any litigation activity.

US Patent 4,812,820 — Analyst Summary

Ground truth note: All identifiers below are taken literally from the authoritative full text and from live sources fetched today (Google Patents, EPO Global Patent Index, uspto.report). I found no CAFC 2026 docket activity naming this patent — see "Litigation search" below.

1. Bibliographic Data

2. Abstract (verbatim)

"A transceiver unit for an electronic surveillance system is internally coded with an address-number for identification within the system and is adapted to receive input from sensors detecting alarm conditions. The unit is switchable from an idle condition wherein it transmits digital data relevant to its address-number and status but does not recognize input from a sensor, to a primed condition wherein it transmits digital data relevant to its address-number and status information indicating an alarm condition. The unit is able to receive digital data from other similar units sequentially and display information relevant to the identity and status thereof. In a security system a plurality of such units communicate with each other and in turn transmit the digital data to all the other units of the system simultaneously, either by hard wiring thereto, radio link or other transmission medium. An alarm condition detected by one unit is recognized at all other units of the system. Remote switching of a unit from idle to primed by any of the other units is disclosed."

3. Plain-Language Overview of the Independent Claims

The patent has 13 claims. Only claim 1 (system) and claim 11 (unit) are independent; claims 2–10 depend from claim 1, and claims 12–13 depend from claim 11.

Claim 1 — The system (peer-to-peer, round-robin, self-supervised)

A surveillance system with several transceiver units at spaced locations. Each unit:

• Transmits in turn — it gets its own exclusive time slot in a repeating cycle, and sends digital data to all the other units at once (a "broadcast" on a shared medium).
• The data identifies which unit is transmitting and carries status information.
• Each unit always listens and can recognize a transmission from any other unit; specifically it recognizes the transmission from the unit immediately ahead of it in the cycle, and then takes its own turn to transmit next.
• The last unit in the cycle sends a coded end-of-cycle signal so the first unit knows the cycle is over and starts again.
• Every unit reacts to failures — if any unit fails to transmit in its turn — and reacts to the status information it receives.

Plain language: A token-passing / round-robin alarm network where each box "checks in" on schedule, everyone hears everyone, and the group self-polices for missing check-ins.

Claim 11 — The transceiver unit itself

A single transceiver unit comprising:

• Means for frequently and periodically transmitting digital data identifying its own address number.
• Means for operating in a primed condition — actively wired to one or more alarm sensors — and transmitting the status of each such sensor.
• Means for switching from primed to idle, where in idle it still transmits its address-number and status but ignores sensor inputs.
• Means for receiving data sequentially from other similar units and displaying the address and status of any unit that fails to transmit or that is in alarm.
• The unit is programmable to "listen" continuously through two consecutive phases:
  1. a report phase, in which it makes its own address/status transmission upon initiation, and
  2. a command phase, in which it counts a predetermined number of timing intervals and can receive an instruction telling it to perform some action.

Plain language: One node of the network, with a "vacation/armed" switch, a display that flags silent or alarming neighbours, and a periodic command window that lets a remote user tell it to do something (per claim 12, e.g., switch from idle to primed).

Notable dependents (context for the independents)

• Claim 2 – display identifies the failing unit plus a fault code, or the reporting unit plus its status.
• Claims 3–5 – status covers alarm conditions from sensors (intrusion/fire; or machine-function monitoring).
• Claims 6–8 – a unit detecting the preceding unit's failure proceeds with its own transmission; a real-time clock resets after each valid round (and after its own transmission) to keep all units synchronized long-term.
• Claim 9 – defines the report phase vs. the command phase (the latter allows an instruction from any unit to any other).
• Claim 10 – idle vs. primed states.
• Claim 12 – the received action is "switch from idle to primed" (remote arming).
• Claim 13 – hardware recitation: microprocessor 11, program ROM 12, interface 17, display 14, digital logic, crystal oscillator 15 — matching the 8031-based embodiment (IC1 8031, IC3 2732 ROM, IC2 74LS373, IC4 8155, IC5 26LS31/IC6 26LS32 RS-422 pair, IC7 MM5450 display driver, IC8 74C922 keyboard encoder).

4. Technical Highlights Worth Flagging

• Communication medium is flexible: twisted-pair hard wiring is the described embodiment; the specification expressly contemplates radio, fibre-optic, or infra-red links (with adjusted timing/baud for narrowband radio).
• Synchronization mechanism: nominal 60 ms per station slot; on each valid status reception the receiving unit reloads its timer T0 to leave 8 ms remaining, and sets its time counter to the received station number.
• Capacity: 16 units (station addresses 0–15), set by DIP switches via IC4 port 27; a 3-digit BCD "user/customer address" via port 28; last station flagged by pulling P3.1-class input P3.5 low.
• Frame structure: report phase + command phase = a "frame," ~1 second, display updated at frame end.

5. Litigation / Docket Search — Result and Uncertainty

• I searched for US 4,812,820 in connection with CAFC 2026 dockets and USPTO records. I found no CAFC (or other court/PTAB) proceeding naming this patent.
• This is consistent with its status: the patent is Expired – Fee Related (anticipated expiration 2006-07-23), and it has no record of assignment to a litigating entity. Given it lapsed roughly two decades ago, 2026 appellate activity is highly unlikely.
• Uncertainty statement: The searches I ran surface patent citations but not a comprehensive court docket database. I could not access a first-party USPTO PatentCenter or CAFC PACER/CM-ECF record directly to conclusively rule out litigation. If you need an authoritative litigation clearance, a direct PACER/CM-ECF docket query and a USPTO Patent Assignment Search are required. I am flagging this rather than asserting a negative with false confidence.

Correctness caution: Do not conflate this patent with similarly-numbered documents. Live results also returned an unrelated US application/publication US 4,929,387 (a renumbering artifact listed on the Google Patents page), US 4,800,820 (Tomaka, cited in the FreightCar America IPR), and unrelated "electronic surveillance" hits such as EP 0440370 and CA 2,039,760 — none of these is US 4,812,820. Only the Chatwin reference corresponds to the requested number.

I'll search litigation databases for US patent 4812820.

Let me search more targeted litigation sources.

Let me verify with a few more targeted litigation sources.

Litigation Search: US Patent 4,812,820

Patent under review (as identified literally in the query): US 4,812,820 — "Electronic surveillance system and transceiver unit therefor," inventor Ian M. Chatwin, filed 1986‑07‑23, granted 1989‑03‑14, priority 1985‑07‑23 (AU PH1606/85). Current record status: Expired – Fee Related (anticipated expiration 2006‑07‑23).

Finding: No litigation identified

Based on my searches of patent‑litigation sources, I found no record of any litigation involving US 4,812,820. I want to be explicit about the limits of this answer rather than manufacture a case list.

What the searches returned

• Google Patents litigation tab / general search: No district‑court or Federal Circuit litigation entries are associated with US 4,812,820. The patent's "Cited By" list is extensive (Icontrol Networks, Sensoria/WINS, Ingrid RFID portfolio, etc.), but citation in later patents is not litigation.
• Unified Patents portal / PTAB: No IPR, PGR, CBM, or other post‑grant proceeding naming US 4,812,820 as the challenged patent. The many "Unified Patents" hits relate to unrelated patents (e.g., US 7,454,002, US 9,046,820) and are not this patent.
• Broader queries ("4812820" + lawsuit/infringement/complaint): Every substantive hit resolved to a different patent whose number merely contains the substring "820" — e.g., US 10,628,820 (CardWare v. Apple/Samsung), US 9,046,820 (Canon), US 9,048,820. None is US 4,812,820. I disregarded these, per your instruction not to return similar numbers.

Case‑list table

Important caveats

1. Coverage limitations. My search relied on web‑accessible aggregators (Google Patents, Justia, Unified Patents portal results, general web). I did not get direct, verified access to PACER docket searches or a full Docket Alarm/RPX litigation‑history pull for this specific patent number in this session. A negative result here should be treated as "not found," not as a definitive "never litigated."
2. Age factor. The patent is a 1986‑filing, fully expired (2006) asset held by an individual inventor. Patents of this vintage are frequently never asserted, and pre‑2000s litigation may be poorly indexed online.
3. Enforcement context (not litigation). The specification emphasizes a neighbourhood‑watch use case and a 16‑unit capacity — consistent with a small, individually owned invention unlikely to generate infringement suits. That is contextual, not evidence of litigation activity.

Recommendation

To close this out definitively, run a direct docket search rather than an open‑web search:

• PACER – search party "Chatwin" and the patent number in the U.S. District Court civil database.
• Docket Alarm / Lex Machina / RPX Insight – query by patent number 4,812,820 (not "820").
• USPTO Patent Center – check the patent's "Litigation" and assignment records for any transfer to an asserting entity.

If you'd like, I can draft the exact PACER search parameters or the Docket Alarm query string. If you have a specific tribunal (e.g., a particular district or the CAFC) in mind, tell me and I can narrow further.

I'll verify the structured data against public sources before writing anything.

Proceedings overview

Zero AIA trial proceedings. The structured PTAB-on-file block reports no AIA trials for US 4,812,820, and independent web searching returned no IPR, PGR, or CBM petition, institution decision, Final Written Decision, or Federal Circuit appeal involving this patent — so the breakdown is simply: active 0 / claims invalidated 0 / claims sustained 0 / settled 0 / institution denied 0, and the defensive posture is not "hardened by surviving IPRs" but rather moot by expiry: US 4,812,820 reached its anticipated expiration on 2006-07-23 and is recorded as "Expired - Fee Related" (https://patents.google.com/patent/[US4812820A](/patent/US4812820A)/en). No defendant today faces live claim exposure, and no third party ever had an economic reason to spend $300k+ challenging a patent whose damages window had already closed before the first IPR was ever filed (IPR/PGR/CBM practice began 2012-09-16).

No proceedings to report

There is no proceeding number to render in the {PROCEEDING_NUMBER} — {Petitioner} v. {Patent Owner} format, and I will not construct one. The sections below explain why the absence is real rather than an artifact, and what it means defensively.

Strategic summary

Claim-status picture. All thirteen claims remain formally unadjudicated by the PTAB — nothing was canceled, nothing was confirmed-in-part, nothing was amended by motion to amend. The claims as granted run 1–13, with claim 1 (system) and claim 11 (transceiver unit) as the independents, and claims 2–10 and 12–13 as dependents. Critically, "untested by IPR" here does not mean "hardened." It means untested because the patent expired. US 4,812,820 was filed 1986-07-23 (App. No. 07/049,293, claiming AU priority PH1606 from 1985-07-23), granted 1989-03-14, and its anticipated expiration is 2006-07-23. Every one of the 13 claims therefore lapsed roughly twenty years ago.

Why no IPR exists — the arithmetic, not the merits. Congress did not create IPR until the AIA, effective 2012-09-16. By that date the patent had been expired for over six years. Under 35 U.S.C. § 286, damages are recoverable only for infringement occurring within the six years preceding the filing of the complaint; because all infringement of this patent necessarily predates 2006-07-23, any complaint filed after approximately 2012-07-23 — i.e., every complaint that could ever have existed after PTAB jurisdiction existed — is worth $0 in recovery. There was never a rational petitioner. The same logic disposes of PGR (unavailable pre-AIA) and of CBM, which in any event this patent does not resemble: its subject matter is CPС G08B27/003, "Signalling to neighbouring houses," a hardware-level neighbourhood-watch alarm system, not a financial-services data-processing claim. I found no evidence of any CBM petition, and no CBM petition would have been available on these claims.

Estoppel landscape — the upside of zero IPRs. Because no IPR was ever instituted, § 315(e)(2) estoppel does not attach to anyone. There is no petitioner, no privy, and no "grounds raised or reasonably could have been raised" bar. For a defendant (or more realistically, a prospective reexamination requester) the entire universe of art remains available in a district court or ex parte reexamination context:

• The six references the examiner cited (https://patents.google.com/patent/US4812820A/en): US 3,909,826 (Schildmeier, plural transceiver alarm system with coded alarm message and every-station display of alarm origin); US 4,400,694 (Wong); US 4,367,458 (Ultrak, supervised wireless security system); US 4,661,804 (Sentrol, supervised wireless security system); US 4,673,920 (General Signal, fire alarm control and emergency communication); US 4,647,914 (Mitsubishi Electric America, security apparatus and system). Note that US 4,909,826's "every station displays alarm origin" teaching is squarely adverse to claim 2 of the '820 patent, and the two "supervised" wireless security system references are adverse to claims 6–8 (missing-transmission detection and synchronism).
• The seven family-cited documents, including DE 2 844 400 A1 (Licentia — multi-transmitter radio network co-ordination by coding and station identification to avoid simultaneous transmission) and GB 2 149 543 A (Morrison, alarm system), which speak directly to claim 1's exclusive-time-slot, in-turn transmission architecture.
• The large body of citing art (Google Patents lists 152 cited-by entries in the summary table, expanding to roughly 315 in the full list), which is a ready source of obviousness combinations.

Pattern signals. None of the usual ones are present. No serial petitioner exists; no Unified Patents or other defensive aggregator has ever touched this patent; the patent owner (inventor Ian M. Chatwin, listed as an individual assignee, never a corporation) never had a PTAB appeal because it never had a PTAB trial. The foreign counterparts ran their ordinary course: EP 0 231 291 B1 granted 1993-04-14 and is recorded as expired / not-active across the family, AU 595 227 B2 "Ceased," CA 1 272 773 A "Expired," with JP S63-500619 A still listed as pending/active in the ODP family table — that JP entry is a family-status artifact, not a US proceeding, and I would not rely on it without checking JPO directly.

Recommended next steps

1. Treat any demand letter asserting these claims as facially deficient on its face. The dispositive fact is not a PTAB outcome — it is the expiration date. Under § 286, no infringement occurring after 2006-07-23 is actionable, and no complaint filed on or after approximately 2012-07-23 can recover anything. Ask the sender to identify (a) the allegedly infringing act, (b) its date, and (c) the date the earliest complaint asserting this patent was served. If (b) postdates 2006-07-23, the demand is empty; if a previous complaint was served more than six years before any new filing, § 286 bars recovery entirely.
2. Verify the "no proceedings" conclusion directly at the source rather than relying on the ODP block or my searches. Confirm on USPTO PTAB E2E (https://ptab.uspto.gov/) by searching the patent number under "Proceedings," and cross-check the CAFC docket and CourtListener (https://www.courtlistener.com/) for any appeal naming US 4,812,820. My searches returned no hits on any of these axes, but search absence is weak evidence and the ODP ingest lag the prompt flags is real; a ten-minute E2E confirmation closes the loop.
3. If, contrary to the above, some proceeding surfaces, the fallback analysis is favorable anyway. Pre-expiration IPRs on long-expired patents are construed under Phillips rather than the BRI standard, and the examiner-cited "supervised wireless security system" pair (US 4,367,458; US 4,661,804) plus Schildmeier (US 3,909,826) and Licentia (DE 2 844 400 A1) map onto independent claims 1 and 11 and onto the missing-transmission and synchronism features of claims 6–8. Flag any such filing to me immediately and I will re-run the claim-level analysis.
4. Check for any live district court assertion before doing anything else costly. If a complaint naming this patent is pending, the correct first move is a § 286 / expiration-based motion or a 12(b)(6), not an IPR — there is no claim left to invalidate and no validity fight worth funding.

Caveat on confidence: I am highly confident the patent is expired and that no AIA trial exists on the ODP record; I am less than certain that no obscure, early-filed petition (2012–2014 vintage, since-terminated) exists outside the indexed sources. That is the one fact worth an E2E check before you rely on this memo in a filing.

I'll verify the assignment record before writing anything. Let me check the primary sources.

No assignment records surfaced yet. Let me probe the USPTO assignment API directly and cross-check a few secondary sources.

Inventors

Unusual patterns. The "all inventors depart within 12 months" tell is inapplicable — there is exactly one inventor, and he never assigned the case away. What is notable is the reverse pattern: a single named individual holding an unassigned, self-filed patent through an Australian agent, in a classification (G08B 27/003, "signalling to neighbouring houses") that is otherwise dominated by corporate filers. There is no portfolio here to fire-sale — one patent, one inventor.

Original assignee

No entity is named as assignee. Google Patents lists both Original Assignee and Current Assignee as "Individual." The issued patent remained the personal property of Ian Malcolm Chatwin throughout.

• Primary line of business: none identifiable. The specification is a design disclosure, not a corporate product brief.
• Product embodying the claims: No evidence found of any commercial product. The claims are device claims — claim 13 recites concrete hardware (a microprocessor 11 with program ROM 12, interface 17, display 14, digital logic and a crystal oscillator 15), and the FIG. 2 embodiment is built from an 8031 (IC1), a 2732 EPROM (IC3), a 74LS373 latch (IC2), an 8155 PPI (IC4), a 26LS31/26LS32 RS-422 pair (IC5/IC6) and an MM5450 display driver (IC7). This is a genuine, buildable neighbourhood-watch alarm, but I found no retail product, manufacturing entity, or catalogue evidence. Treat "no product shipped" as not established either way rather than proven.
• Current status: there is no corporate assignee to be operating, acquired, dissolved, or in bankruptcy. The patent itself expired for failure to pay maintenance fees, anticipated expiration 2006-07-23, legal status "Expired – Fee Related." I have no information about the inventor's current circumstances and will not speculate.

Assignment timeline

The USPTO assignment record for US 4812820 contains no records. Plainly stated: this patent has no recorded assignments — not an original-to-inventor assignment, not a post-issuance transfer, nothing. Ownership never moved from the sole inventor.

Verification basis and its limits: Google Patents' bibliographic record for US4812820 shows no AS (Assignment) legal event of any kind, and lists the assignee as "Individual." That is supportive but not a substitute for the register itself — I was unable to execute a live authenticated query against assignment-api.uspto.gov/patent/lookup in this session, so treat the null result as high-confidence but independently re-verifiable rather than certified by me. Confirm at USPTO Assignment Center (search 4812820) and the mirrored assignment.uspto.gov.

What is recorded is bibliographic prosecution data, not conveyance:

• 1986-07-23 — Application US 07/049,293 filed (national stage of PCT/AU86/00209; § 371(c) date 1987-03-18; § 102(e) date 1987-03-18).
• 1989-03-14 — Patent granted.
• 2006-07-23 — Anticipated expiration; patent expired for non-payment of maintenance fees.

Correspondent of record. The only representative named anywhere in this chain is the PCT agent: SANDERCOCK, SMITH & BEADLE, 207 Riversdale Road, Hawthorn, VIC 3122, Australia (per WO 87/00711). Be precise about what that is: prosecution representation, not an assignment-recording correspondent. There is no assignment correspondence to compare it against, so the "repeat correspondent across the chain" test has nothing to operate on here. No US correspondent is identified in the sources available.

I am carrying on to the remaining sections rather than stopping here, because your own verdict rubric explicitly contemplates the no-records case ("Insufficient data") and cannot be answered without them.

Timeline diagram

timeline
    title Ownership of US 4812820
    1985 : AU priority PH1606 filed by Chatwin
    1986 : PCT application filed by sole inventor
    1987 : US national phase entered under 371
    1989 : US patent granted to Ian M Chatwin
    2006 : Patent lapses for unpaid maintenance fees

NPE / troll-pattern signals

Assessed against a null assignment record. Several signals are structurally incapable of being "present" here — that is a finding, not a gap in the analysis.

1. Shell-entity transfer — not present. No transfer of any kind occurred. There is no "IP / Patents / Licensing / Holdings / Ventures" entity, no registered-agent service address, no single-member LLC anywhere in the chain. The assignee of record is a natural person in East Brighton, Victoria.
2. Known asserter in the chain — not present. None of Acacia, Marathon, IV, IPNav, Wi-LAN, Mosaid/Conversant, Vringo, Pendrell, Innovatio, MPHJ, Lumen View, Round Rock, Document Generation Corp, or any Spangenberg vehicle appears. All had to appear by recorded assignment; there is none.
3. Repeat correspondent across the chain — not present. With zero assignment records there is no chain of recordings and therefore no recurring recording attorney to detect. Sandercock, Smith & Beadle appears once, as foreign prosecution agent on the PCT. A single appearance is not the signal — as your instructions note, recurrence is the signal, and recurrence is absent.
4. Cascading transfers — not present. Zero assignments in 20 years of enforceability cannot satisfy "multiple consecutive assignments in <24 months."
5. Pre-litigation transfer — not present. No assignment exists within six months of any suit; indeed no infringement litigation naming this patent surfaced in my searches. The patent lapsed in 2006, which forecloses future assertion entirely.
6. Bankruptcy fire-sale — not present. No Chapter 7/11 proceedings involving any assignee, because there is no corporate assignee. The patent's end came from failure to pay maintenance fees (anticipated expiration 2006-07-23; status "Expired – Fee Related") — an abandonment, not an asset sale.
7. Privateering — not present. No operating-company-to-NPE transfer exists, and no operating company was ever in the chain.
8. Defensive aggregator — not present. RPX, AST, LOT, Unified and OIN do not appear. Note the distinction from the inverse signal you defined: this patent is functionally neutralised by expiration, not by acquisition into a defensive pool. Signature is waiver of maintenance fees, not an RPX reel/frame.

One adjacent observation worth recording, carefully bounded. US4812820 is cited as background art across a very large modern premises-security family — the Google Patents citation set shows it cited by 152 documents, overwhelmingly the Icontrol Networks / Comcast/Cable Communications continuation families on networked security panels and sensor meshes. Same classification, same problem space. But citation is not ownership, assertion, or control. It appears as prior art only; it never appears as an asserted patent or a transferred asset. Do not let the citation density read as NPE activity — it is the opposite: a dead 1989 individual patent sitting in the background-art stack of a later corporate patent war.

Verdict

Insufficient data — the rubric's "no records" case, applied exactly.

There are no recorded assignments: the chain is a single natural person, Ian Malcolm Chatwin, from the 1986-07-23 filing through the 1989-03-14 grant to the 2006-07-23 fee lapse, with no AS legal event in the Google Patents record and no LLC, aggregator, or known asserter anywhere in the family (EP0231291B1, JPS63500619A, AU595227B2, CA1272773A, ATE88306T1, DE3688286D1). Every NPE signal above is "not present" for the simple structural reason that no transfer ever happened. The single materially useful conclusion is the inverse of a troll finding: this patent is neutralised by expiration, lapsed for unpaid maintenance fees roughly seventeen years after grant, and is not assertable today.

Verification: USPTO Assignment Center — search 4812820; Google Patents record.

Caveat on my sourcing: I did not obtain an authenticated live response from the Assignment Center or the ODP assignments endpoint during this session. My null result rests on the absence of any assignment legal event in the indexed record and on the assignee-of-record being a natural person. Before this is used for any diligence purpose, re-run the query directly against assignment-api.uspto.gov/patent/lookup and confirm the empty set.

I'll research the cited prior art for US 4,812,820, verifying each reference against live sources.

Let me research the remaining cited references.

Prior-Art Analysis for US 4,812,820

Ground-truth note. I confirmed the identifier literally as US 4,812,820 A ("Electronic surveillance system and transceiver unit therefor," Ian M. Chatwin) against the authoritative full text and live sources. All six examiner-cited references below are taken from the patent's own "Patent Citations (6)" table (each marked "* Cited by examiner"), and each was independently checked against Google Patents / uspto.report. Dates are given exactly as they appear in the patent and are consistent with the live records. No contradiction with the previously generated summary's prior-art list — it matches.

One process caveat up front: I retrieved substantive text for five of the six references (US 3,909,826; US 4,367,458; US 4,400,694; US 4,647,914; US 4,661,804). I was not able to pull the full specification of US 4,673,920 (General Signal) in this session, so its description below relies on its title/assignee/prosecution listing and is flagged as lower-confidence.

1. The six examiner-cited references (of record)

Sources: patent "Patent Citations (6)" table; https://patents.google.com/patent/US3909826, .../US4367458A, .../US4400694, .../US4661804, .../US4647914; PDFs at patentimages.storage.googleapis.com/.../US3909826.pdf, .../US4661804.pdf, .../US4647914.pdf.

2. Reference-by-reference: description and §102 claim mapping

A. US 3,909,826 — Schildmeier (1975)

Description. A peer-to-peer neighbourhood radio alarm: "a plurality of alarm units remote from one another," each containing a sensor/trip switch, coding means producing a coded electrical signal unique to the alarm unit, a radio transmitter, and a receiver + decoder + display that indicates which other unit originated a received alarm (see PDF text: "each unit serves as an alarm receiver as well as an alarm transmitter without physical connections… display means… for indicating the specific decoded radio frequency signals received"). Trip switch may be wired remote; an additional trip switch can detect fire.

Why the examiner cited it: it is the closest "plural transceivers, each identifying itself, all stations display the alarm origin" system.

§102 mapping / gaps:

• Discloses: "plurality of transceiver units at spaced locations"; data identifying the transmitting unit; reception of transmissions from any other unit; display of alarm origin — i.e., the concepts underlying claim 2 ("displaying information identifying said one unit and the status thereof") and the abstract.
• Missing for claim 1: no round-robin sequential time-slot cycle, no element that identifies the immediately preceding unit and transmits next in turn, no last-unit end-of-cycle code, and no failure-to-transmit detection. (Alarm transmission is event-driven, not periodic.)
• Assessment: does not anticipate independent claim 1 (or 11). It is best treated as §102 art only against a hypothetical bare "each unit identifies itself and all stations display origin" claim, which is not what claim 1 recites.

B. US 4,367,458 — Ultrak (1983)

Description. Supervised ultrasonic wireless security system. A central control unit (CDU) "periodically transmits an interrogation code to all transponders; each remote unit responds if all is well. If a unit does not respond, an alarm is initiated." Each transponder carries a unique built-in coded identification number; it emits an unsolicited response on intrusion or low battery; failures and low-battery conditions are displayed with the identity number of the unit.

§102 mapping / gaps:

• Discloses: periodic/sequential interrogation, unit identity codes, supervision = detecting a unit that fails to respond (→ the "respond to the failure of any one unit… to transmit" concept; cf. claims 2, 6, 7), status reporting (intrusion/fire/emergency/low battery), and identity display.
• Missing for claims 1 and 11: it is a star topology with a single master CDU, not a peer-to-peer cycle in which each unit recognizes its immediate predecessor and self-sequences, and there is no end-of-cycle code from a "last" unit.
• Assessment: strong §102 art against the supervision/failure-detection and identification limitations, but does not anticipate claims 1–10 or 11 as a whole.

C. US 4,400,694 — Wong (1983)

Description. A microprocessor-based monitor/control "base" for a communications facility (telephone/technical control facility): an Input/Output Control Computer (IOCC) with two parallel microprocessors, and Monitor-and-Alarm Processors (MAPs) at repeater stations that process alarms and monitoring functions, signal the IOCC via interrupt control, and store data in mass storage.

Why cited: general microprocessor/ROM/memory architecture for alarm monitoring, and it directly parallels the claim 13 hardware recitation (microprocessor → ROM/RAM, ports, interrupt-driven monitoring).
§102 mapping / gaps: relevant only to claim 13-type structural recitations and general alarm processing; it discloses no neighbourhood peer-to-peer transceiver network and no round-robin sequencing. Does not anticipate claims 1 or 11.

D. US 4,661,804 — Sentrol (1987)

Description. Supervised radio-linked alarm system. Each transmitter is pre-settable with a digital system address and channel address; a receiver-decoder rejects nearby similar systems, validates messages, and routes them by channel address. Receipt of a valid message resets a per-channel timer; failure to receive within a preset time triggers a maintenance-warning indication identifying the specific transmitter. It expressly frames the problem of mutual RF interference when transmitters share one frequency and the need for a "schedule system to avoid simultaneous transmissions."

§102 mapping / gaps:

• Discloses: periodic individually-identifiable transmissions, per-transmitter supervision/timer, failure-to-receive → maintenance warning (→ claims 2, 6, 7 concepts), and the problem statement motivating scheduled/time-slotted transmission.
• Missing for claims 1/11: it is a one-way transmitter → central receiver-decoder architecture ("one-way flow of information"), not a peer-to-peer cycle where a unit identifies its predecessor and transmits next, and there is no last-unit end-of-cycle code.
• Assessment: highly relevant §103 (and partial §102 against the supervision/identification limitations); does not anticipate the independents.

E. US 4,673,920 — General Signal (1987) — lower confidence; full text not retrieved

Description (from title/prosecution listing). A fire-alarm control and emergency communication system assigned to General Signal Corporation (a major fire-alarm controls manufacturer). By title/classification it concerns central alarm control with multiplexed/emergency signalling to remote stations.
§102 mapping / gaps: consistent with the claim 9 "report phase / command phase" and central control concepts, and with alarm-status reporting; but a central fire-alarm control panel is not the claimed distributed peer-to-peer round-robin. I did not verify its disclosure element-by-element and therefore cannot responsibly map it to specific claims beyond noting its general field. Treat this one as unverified.

F. US 4,647,914 — Mitsubishi Electric America (1987)

Description. "User friendly" home/small-business security apparatus and system: small-RF transmitters broadcast a facility code + zone code; a console transponder receives them and autodials a central monitoring service. The transponder "operates in an armed or idle operational mode" with a key-actuated arm switch, plus test/reset in idle mode.

§102 mapping / gaps:

• Discloses: the idle vs. armed/primed mode distinction (→ claim 10 and the "primed/idle" language of claim 11), facility/zone codes, and status display.
• Missing: it is a master/console + one-way sensor transmitters system dialing a remote central service; no peer-to-peer cycle, no predecessor-identification, no end-of-cycle.
• Assessment: good §102 art against the idle/armed-mode limitations; does not anticipate claims 1 or 11.

3. Bottom line on §102

• No single one of the six references anticipates independent claim 1 or claim 11. Each is missing at least the defining "self-sequencing round-robin" elements of claim 1 — (i) transmission in turn at an exclusive time slot in a cycle, (ii) recognizing the immediately preceding unit and transmitting next in turn, (iii) the last unit's coded end-of-cycle signal letting the first unit recommence. This is precisely the point of novelty over A (peer-to-peer but event-driven) and over B/D (periodic but master-star), and it is why the patent issued over these references.
• Highest-value §102 art for individual limitations:
  • Claim 2 (identity + fault/status display): A (origin display), B and D (identity + supervision display).
  • Claims 3–5 (alarm types / fire / machine monitoring): A, B, D.
  • Claims 6–7 (proceed on predecessor failure; real-time clock resynchronization): B and D (supervision timers) — nearest, but neither resets a peer clock from a predecessor's transmission.
  • Claims 9 / 11 command-phase (count timing intervals; receive instruction): not squarely met by any of the six; E is topically closest (central control) but unverified.
  • Claim 10 / claim 11 primed-vs-idle: F (armed vs. idle mode).
  • Claim 13 (microprocessor + ROM + interface + oscillator): C.

I am flagging this explicitly: the appropriate use of all six references is as §103 obviousness art (and as support for narrow dependent limitations), not as §102 anticipation of the independent claims.

4. Additional prior art of record — foreign "Family Cites Families" (7)

The prosecution/family search reports also cited these (from the patent's "Family Cites Families (7)" table); they bear on the same round-robin/neighbourhood-alarm issues:

Two of these are especially notable for the §102/§103 story: DE 2,844,400 (Licentia) — "reduces probability of simultaneous transmission by coding and identification of station for priority rating" (i.e., contention/time-slot coordination), and JP S58-124347 (Hitachi) — a loop-shaped local network (ring topology, the conceptual ancestor of token/round-robin passing). AU 42822/85 (Hansen, "Neighbourhood alarm") is the closest neighbour-alarm concept. I have not yet pulled their full texts, so I do not assert element-by-element anticipation; they are listed as art of record for completeness.

5. Caveats and confidence

• Verified: US 4,812,820 identity, its six examiner citations, and their bibliographic data (cross-checked against Google Patents and uspto.report).
• Unverified: full disclosure text of US 4,673,920 (General Signal) — I could not retrieve it in this session, so its claim mapping is limited to its title/field.
• Not performed: element-by-element claim charts for the seven foreign family citations.
• Legal standard reminder: §102 requires a single reference to disclose every element of a claim, arranged as claimed. Because none of the six references contains the full round-robin self-sequencing combination of claim 1, none anticipates the independents; combinations with the foreign art (notably Licentia and Hitachi) are the more realistic invalidity theory, and that is a §103 question.

If you want, I can pull the full specifications of US 4,673,920, DE 2,844,400 and JP S58-124347 and build a formal element-by-element claim chart against claim 1 and claim 11.

I'll research the cited prior-art references to ground the §103 analysis.

Let me get the remaining references, including those cited in the international family.

Obviousness Analysis — US 4,812,820 under 35 U.S.C. § 103

Scope note / contradiction flag. Two dates appear in my instructions: the operating date "2026‑09‑30" (patent text header) and "Current Date: April 26, 2026" in this task. I flag this rather than silently pick one; it does not affect the analysis. Second, this is a technical/legal analysis of the prior-art record on this page, not a validity opinion or legal advice. Third — important — I retrieved full/abstract text for only some of the cited references (details below); where I could not, I rely on the literal titles and bibliographic data exactly as they appear in this page's Prior Art section, and I say so.

Per your instruction, I use the Prior Art section of this page, which consists of:

• Patent Citations (6) — all marked "Cited by examiner": US 3,909,826; US 4,367,458; US 4,400,694; US 4,647,914; US 4,661,804; US 4,673,920.
• Family Cites Families (7) — US 2,663,864; US 4,019,139; DE 2,844,400; JP S58‑124347; JP S60‑10939; GB 2,149,543; AU 4282285.

(Later "Cited By" art is after-arising and is not usable for §103 against this patent.)

1. Legal framework applied

Under Graham v. John Deere and KSR Int'l v. Teleflex, the inquiry is: scope/content of the prior art, differences from the claims, PHOSITA level, and secondary considerations. KSR supplies the combination rationales I apply below: (A) familiar elements combined with known methods yielding predictable results; (B) substitution of a known element; (C) known technique improving a similar device in the same way; (D) applying a known technique to a known device ready for improvement; (E) "obvious to try" from a finite set of predictable solutions; and (F) design incentives/market forces.

PHOSITA (c. 1985): a technician/engineer in microprocessor-based alarm and data-communications systems, familiar with the 8031/8155/RS‑422 families recited in claim 13 and with multiplexed/polled alarm loops.

2. Claim 1 decomposed, with an element‑to‑reference map

Claim 1's independent elements and where the record supplies them:

Read-out: no single reference contains every element — this is why the claims issued. But each element is independently known, and the record contains express motivations to combine (see §4).

3. What the closest references actually teach (grounded)

• US 3,909,826 — Schildmeier (filed 1973‑08‑31; granted 1975‑09‑30), "Plural transceiver alarm system using coded alarm message and every station display of alarm origin." This is the closest single reference. It discloses a plurality of units on different premises, each serving "as an alarm receiver as well as an alarm transmitter without physical connections," each coding a signal "unique to the alarm unit," and each displaying the origin of an alarm received from any other unit. Its own background even describes a wired neighbourhood system where "each unit… receive[s] an alarm signal from any unit detecting an emergency condition." Source: https://patents.google.com/patent/US3909826
• US 4,367,458 — Ultrak (Hackett) (1980/1983), "Supervised wireless security system." Explicit periodic interrogation; "each remote unit responds if all is well. If a unit does not respond, an alarm is initiated"; transponders carry "unique identification number"; summary states "failures of particular units of the system [are] reported." Sources: https://patents.google.com/patent/[US4367458A](/patent/US4367458A) ; https://portal.unifiedpatents.com/patents/patent/US-[4367458](/patent/4367458)-A
• US 4,661,804 — Sentrol (1982/1987), "Supervised wireless security system." Preset system+channel addresses; messages carry sensor state; "Failure to receive a message allows a preset time to elapse, after which a maintenance requirement warning is provided." Source: https://patentimages.storage.googleapis.com/6e/ea/cb/b81f5446f83fb7/US4661804.pdf
• US 4,673,920 — General Signal (1984/1987), "Fire alarm control and emergency communication system." Distributed, no‑master, peer architecture: each node "communicate[s] with four adjacent nodes," forwards status to adjacent nodes, "no one node ha[s] priority over any other node," and any node can "act as a control center." Source: https://patents.google.com/patent/US4673920
• US 4,400,694 — Wong (1979/1983): microprocessor base monitoring alarms by interrupts/ID codes — supports the microprocessor implementation of claim 13.
• US 4,647,914 — Mitsubishi Electric America, "Security apparatus and system" (1984/1987) — additional multi-unit security systems art. (Full text not retrieved; characterized from the page's literal title.)
• DE 2,844,400 — Licentia: "Multiple transmitter radio network coordination system — reduces probability of simultaneous transmission by coding and identification of station for priority rating." This is the express teaching of scheduled/ordered transmission with station ID on a shared channel. (Title/bibliographic data only.)
• JP S58‑124347 — Hitachi, "Loop‑shaped local network"; JP S60‑10939 — NEC, "Data transmission equipment"; GB 2,149,543 — Morrison, "Alarm system"; AU 4282285 — Hansen, "Neighbourhood alarm"; US 4,019,139 — Ortega, "Interaction multi‑station alarm system"; US 2,663,864 — Cundiff, "Electric burglar alarm system." (Titles/metadata only.)

4. Proposed §103 combinations

Ground 1 — Claims 1–5, 10: Schildmeier '826 + Ultrak '458 (and/or Sentrol '804)

Schildmeier supplies the dispersed multi‑unit coded alarm network with per‑unit identity, mutual reception, and origin display. Ultrak supplies periodic supervised status reporting and failure‑to‑respond → alarm/identity display; Sentrol supplies address‑coded status messages and failure‑to‑receive → warning.

• Motivation (KSR (C), (F)): Both firms target the same problem — knowing which protected location is in trouble and knowing when a unit has silently failed. Ultrak's stated aim, to report "events such as intrusion, fire or emergency as well as failures of particular units," is precisely the object of claim 1's last two elements. A PHOSITA would apply supervision to Schildmeier's network to obtain the predictable benefit of fault detection.
• Predictable result (KSR (A)): Combining broadcast alarm messaging with cyclic status polling is the routine aggregation of two known alarm‑system schemes; no new operational principle arises.

Ground 2 — Claim 1 (and 6–9): Ground 1 + General Signal '673,920

Adds the no‑master, node‑to‑adjacent‑node, stand‑alone peer topology and orderly propagation — supplying the "transmit next in turn," "immediately preceding unit," and "last unit → first unit recommence" features (ring/loop wrap).

• Motivation: General Signal expressly eliminates the master controller ("no one node having priority") to avoid single‑point failure; that is the same design incentive driving the patent's peer‑to‑peer claim. Combining it with a shared channel yields a self‑organized round‑robin — the claimed cycle.

Ground 3 — Claim 1: Ground 2 + DE 2,844,400 (and JP S58‑124347)

DE 2,844,400 is the missing motivational keystone: it addresses exactly the problem of multiple transmitters sharing a medium and transmitting simultaneously, and solves it by coding and station identification for ordered/priority access — i.e., assigned slots. Loop‑network art (JP S58‑124347) supplies ring ordering.

• Motivation (KSR (D), (E)): Applying a known channel‑coordination technique (TDMA/slotting with station IDs) to a known multi‑unit alarm network "ready for improvement" is the paradigm KSR case; there is a finite, predictable set of solutions (slot assignment / ring token) and a clear reason to pick it (avoid collisions, assure each unit a guaranteed check‑in window).

Ground 4 — Claims 11–13: Ground 1 + Wong '440,069 (+ Ultrak's interrogation/remote‑keypad)

• Claim 11's report phase maps to '826/'458/'804 status reporting; its command phase ("count a predetermined number of timing intervals and… receive an instruction") maps to Ultrak's CDU interrogation cycle and remote keypad, and to Wong's microprocessor monitor/control base with command/ID handling.
• Claim 13's hardware (µP + ROM + interface + display + digital logic + crystal oscillator) is the conventional microprocessor alarm node of Ultrak/Wong.
• Motivation: the patent's own stated problem — "false alarms… causes a major inefficiency of these 'base station' systems," and neighbours forgetting to arm — is a recognized market need pushing toward a status/command window on each node.

5. Claim‑by‑claim disposition (tentative)

6. Where the patent would likely resist §103

I should be candid about the counter‑case, not just the plaintiff's case:

1. The art was before the examiner. All six "Patent Citations" are examiner‑cited and appear on the face of the patent. A challenger relying only on those must show the examiner overlooked the combination — a meaningful hurdle, since the grant date (1989‑03‑14) post‑dates every cited reference.
2. The critical two references may be foreign‑family cites, not US‑of‑record. DE 2,844,400, JP S58‑124347, JP S60‑10939, GB 2,149,543, AU 4282285 and US 4,019,139 appear under "Family Cites Families," i.e., cited in EP/AU/JP family members. Whether they were before the US examiner is not established by this page — so a challenger using DE 2,844,400 as the slotting teaching may face a "not of record" question, while simultaneously gaining freedom from the "already considered" inference. I cannot resolve this from the page alone; a front‑page/full‑file‑wrapper check is required.
3. No single reference anticipates. Each element is distributed across at least three references, and the self‑organizing aspects — (a) recognizing the immediately preceding unit and taking the next slot without a master, and (b) the last unit's end‑of‑cycle code enabling the first to restart — are not squarely shown in the text I retrieved. The closest ('673,920) shows adjacent‑node forwarding, not a broadcast‑medium token cycle; DE 2,844,400 is only characterized here by its title. A challenger must build these from titles/metadata plus general knowledge, which is a softer record.
4. Claim 12 (remote peer arming) has no direct read in the retrieved texts: Ultrak's remote keypad arms its own CDU; the patent claims one unit commanding another to switch idle→primed. This is the most defensible increment.

7. Bottom line

• Most probable §103 ground: US 3,909,826 in view of US 4,367,458 (or US 4,661,804), further in view of US 4,673,920, and optionally DE 2,844,400 — with US 4,400,694 for the microprocessor platform.
• Claim 1 and simple dependents (2–5, 10) are the easiest to invalidate; the report/command‑phase unit claims (11–13) are the hardest, chiefly because of the peer‑to‑peer remote‑arm feature and the specific two‑phase timing architecture.
• Strength caveat: because the six domestic references were examiner‑cited and the strongest slotting reference (DE 2,844,400) is a family cite of uncertain US‑of‑record status, this is a plausible but not a clean obviousness case. The decisive next step is verifying, from the US file wrapper and front page, exactly which references were before the US examiner — that single fact materially changes the strength of Grounds 2–3.
• Practical note: the patent is Expired – Fee Related (anticipated expiration 2006‑07‑23), so any §103 challenge today is defensive/moot‑value only — there is no live infringement exposure to invalidate against.

Confidence: High on the claim‑element mapping and on the content of US 3,909,826 / 4,367,458 / 4,661,804 / 4,673,920 / 4,400,694 (full or abstract text retrieved). Low‑to‑moderate on DE 2,844,400, GB 2,149,543, US 4,019,139, AU 4282285, JP S58‑124347, JP S60‑10939 and US 4,647,914, for which I retrieved only the literal titles/metadata shown on the page — any argument turning on those references should be re‑verified against their full texts before being relied upon.