---
type: concept
tags: [parking, devices, monitoring, telemetry]
sources: []
updated: 2026-06-15
status: open
---

# Device Events (telemetry)

The **unsigned** operational record of what the hardware did and reported — distinct from the
signed business [[append-only-event-chain|ledger]] (see [[event-streams-split]]). For monitoring,
diagnostics, and live booth status — **not** anti-fraud.

## What lands here

- **Relays/barriers:** relay fired/released, pulseOpen issued (the *device-side* echo; the
  authoritative `barrier_open_command` is a signed ledger event).
- **Printers:** paper-out / near-end / cover-open / cutter / offline (already polled —
  [[printer-status-monitoring]]).
- **Cameras:** reachable/offline, snapshot success/failure ([[lpr-camera]]).
- **Readers / inputs:** a raw read, raw input edges (Dingtian button `input N on/off` —
  [[device-input-flow]]).

## Properties

- **Unsigned, not chained** — no `prevHash`/`signature`. It's telemetry, so it carries none of the
  ledger's integrity machinery.
- **Disposable** — high-volume and churny; **may rotate/prune** on a retention policy (the ledger
  never does).
- **Device-keyed** — references the `devices` instance (raw device provenance). No `lane`
  (pool-of-spaces model — see [[entry-exit-points]]).

> **Not to be confused with [[app-logs]].** `device_events` is **hardware telemetry** (a relay fired,
> a camera failed). Diagnostic/application logs (a failed API request, an uncaught frontend error,
> a backend warning) are a **separate third stream** in `app_logs` — don't route app errors here, nor
> hardware telemetry there. Both are unsigned + prunable; the distinction is *what produced it*.

## The boundary that matters

A device event is *evidence the host saw something happen*; it does **not** by itself authorize or
record a business fact. A button press here becomes a **signed `vehicle_entry`** in the ledger only
after the entry flow runs (ticket + barrier command). This keeps device chatter on the device side
of the [[device-adapter-pattern|adapter boundary]] and the signed ledger focused on money/access.

## Open

- Retention/rotation policy (size- or age-based).
- Whether any witness-grade device fact (e.g. a loop-sensor `barrier_open_observed`) should *also*
  write a signed ledger entry for [[reconciliation]] — see [[append-only-event-chain]].