Cellular PIR Motion Detector

Senior HW/FW/Backend Engineer — “Cellular PIR Motion Detector” (Ultra-Low-Cost, LTE-M, eUICC, Real-Time Alerts)

Project summary
Battery-powered, outdoor PIR motion detector using LTE-M (Cat-M1) with eUICC-only for remote carrier switching (multi-MNO: Verizon/AT&T/T-Mobile). The device must deliver real-time alerts (no batching) with minimal on-air bytes and rock-bottom BOM.
Core tech: Sequans Monarch 2 GM02S (app-core), Panasonic EKMB PIR, FPC antenna, IP67/68 enclosure, CoAP/UDP (Confirmable) + CBOR/binary payload, RAI + PSM/eDRX, PLMN scan + hysteresis for profile switching via eUICC/SM-DP+.

Responsibilities (end-to-end)
Electronics & RF
Schematic/PCB (Altium/KiCad), single-rail 3×AA Li-FeS₂, supercap burst buffer, ESD/TVS.
RF layout with low-cost FPC antenna; keep-outs/matching within module grant.
Firmware (GM02S app-core)
PIR ISR → debounce → CoAP(CON) POST → piggyback ACK → RAI → PSM.
Binary/CBOR payload (~13–20 B) with PSK-HMAC integrity; IPv4 PDP; no DNS in hot path.
PLMN scan + hysteresis (24h lockout; switch on sustained better RSRP) and hooks to eUICC RSP (SM-DP+) to activate profiles OTA.
Driveway (real-time) and Trap (rate-limited) modes.
Real-time alerting software (no batching, ever)
Build a tiny, stateless CoAP/UDP listener (Go/Rust/Python) that:
ACKs immediately (within a few ms) and validates PSK-HMAC.
Synchronously fans out the same alert to:
SMS (e.g., AWS SNS or Twilio),
Email (AWS SES),
Native app push (FCM/APNs),
Alexa consumer notifications (Proactive Notifications),
Google Home (Home Graph / Home notifications).
Uses in-memory queue only for in-process transient buffering; no scheduled jobs or time-bucket batching in the hot path.
Provides webhooks for optional integrations (e.g., Slack/Teams) executed synchronously after ACK.
Mobile app (lightweight, native-push first)
Ship a minimal cross-platform app (Flutter or React Native) that:
Registers for push tokens (FCM/APNs),
Displays real-time alerts and device health,
Offers a basic settings screen (mode toggle, quiet window, firmware OTA trigger),
Supports provisioning QR (device ID + claim code).
No polling, no batching—push only.
Mechanical & Environmental
Choose a standard IP67/68 enclosure (~120×65×40 mm class) with screw tabs.
PIR lens/window, ePTFE vent, standoffs; assembly notes for –40 °C to hot sun.
Compliance & Manufacturing
FCC Part 15B SDoC (unintentional radiator), RF exposure evaluation, PTCRB host listing, carrier acceptance.
DFM/DFT for low-cost PCBA (JLC/OPL where possible).
Pogo-pad map (VBAT, GND, UART TX/RX, RESET, BOOT; optional SIM ISO pads) for factory eUICC bootstrap and end-of-line test.
Pilot build support (JLC/PCBWay/MacroFab or equivalent).
Deliverables
Schematics/PCB (source + fab data, PnP, drawings), RF app-note (antenna placement/keep-outs).
BOM/AVL with OPL alternatives; target BOM $6–$8 ex-battery.
GM02S firmware with:
CoAP/UDP(CON) minimal packet (~80–100 B on air incl. ACK),
RAI + short T3324, long T3412,
PLMN scan + hysteresis + eUICC profile switch hooks,
Parameter store (quiet window, modes), and OTA update hook.
Real-time fan-out microservice (containerized):
CoAP listener (UDP/5683), immediate ACK,
Synchronous fan-out to SMS/Email/Push/Alexa/Google,
Secrets via env/SSM; structured logs; Prometheus metrics.
Mobile app (Flutter/React Native) with push, device claim, simple settings.
Cloud IaC (Terraform or CDK) for least-cost deploy (2 micro-VMs or small container service; SES/SNS/FCM/APNs, Alexa/Google creds as secrets).
EOL scripts & fixtures: read IMEI/EID, attach test, test CoAP, program bootstrap SM-DP+ profile if needed; PASS/FAIL printout.
Certification pack: pre-scan results, labels/inserts, RF exposure calc, antenna gain statement, PTCRB plan.
Ops docs: profile swap SOP, alarm webhooks, token lifecycle (FCM/APNs), Alexa/Google account setup.
Five Prototypes: 5 commercial and complete working prototypes ready to be sent for FCC and field testing.
Real-time & data SLAs (acceptance criteria)
Hot path latency (device → SMS/Push/Email/Alexa/Google):
p95 ≤ 1.0 s, p99 ≤ 2.0 s measured from device transmit to provider API 2xx/accepted.
On-air bytes per alert (IPv4): ≤ 100 B total (uplink + ACK) in driveway mode.
Power behavior: during 1 Hz bursts, modem stays in Active-Time (T3324 ~10–15 s); RAI after final ACK; PSM otherwise.
Carrier switching: device switches only on sustained improvement (≥ 8 dB RSRP for ≥ 10 min), with a 24 h hold-off.
Must-have experience
Shipped LTE-M/NB-IoT battery devices using PSM/eDRX and RAI.
eUICC (SM-DP+, LPA, profile management) and multi-carrier deployments.
CoAP/UDP, CBOR/binary payloads, FCM/APNs, SES/SNS, Alexa Notifications, Google Home.
RF layout with low-cost FPC/PCB antennas in plastic enclosures.
FCC Part 15B/EMI pre-scans, PTCRB/carrier processes.
DFM/DFT with low-cost assemblers (JLC/Seeed/PCBWay/MacroFab).
Nice-to-haves
Sequans Monarch 2 SDK experience.
Go or Rust for high-perf UDP services.
IoT cost-down using OPL parts; EVT/DVT/PVT leadership.
Clarifying questions (please answer in your proposal)
Preferred language for the CoAP listener (Go/Rust/Python) and your chosen push providers (SNS/SES vs Twilio/SendGrid).
Prior work samples showing sub-second end-to-end alert fan-out.
Proposed enclosure and antenna you’d start with (SKU/links).
Which eUICC provider(s) you recommend and your experience integrating SM-DP+.
Estimated NRE (HW/FW/Cloud/App) and timeline to EVT/DVT.

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