---
type: concept
tags: [parking, safety, devices]
sources: [parking-system-architecture]
updated: 2026-06-14
---

# Fail-State & Safety (custom controller)

For the [[esp32-custom-controller]], fail-state behaviour is to be treated **as seriously as the
crypto**. (See [[parking-system-architecture]] §7.)

- **Define behaviour on power/network/host loss:** **entry fails closed**, **exit fails open** —
  **never trap a vehicle** (often a legal egress requirement).
- **Hardware manual override** (key switch/button) that opens the barrier **with the ESP32 dead**.
- **Watchdog** with a defined safe default.
- The **barrier operator still owns physical safety** — the ESP32 only signals intent
  ([[barrier-not-a-door]]).

The general "fail-open on exit" principle is also an [[open-questions|open question]] (#2) for
the system as a whole, not just the custom controller.