ESPHome Network & API Watchdog — Auto Power-Cycle with SONOFF S31

Overview

Sometimes devices lock up and need a power cycle. Rather than get up and unplug something, these two ESPHome configurations turn a cheap SONOFF S31 smart plug into an intelligent watchdog that does it automatically.

Two approaches to detecting the same problem — pick whichever fits your situation:

Approach 1 — Ping Watchdog

Gist

Pings a target IP address every 60 seconds. After ping_loss_threshold (default: 3) consecutive minutes of 100% packet loss, it power-cycles the relay. A ping_hold_off timer (default: 5 minutes) prevents it from re-triggering immediately after a cycle.

substitutions:
  target_ip_address: "192.168.20.121"
  ping_loss_threshold: "3"
  ping_hold_off: "5"

Best for: Monitoring a device that should always respond to ping — a NAS, router, server, or network switch. The monitored device doesn’t need to run ESPHome or Home Assistant.

How it works: Uses the AsyncPing external component. A signed int global tracks consecutive failures. When threshold is crossed: relay off → delay → relay on. The manual button on the S31 also triggers a power cycle.

Approach 2 — Home Assistant API Watchdog

Gist

Uses ESPHome’s native api.reboot_timeout. If the ESPHome device loses connection to the Home Assistant API for longer than the threshold, it cycles the relay.

substitutions:
  api_loss_threshold: "17min"

Best for: Monitoring a device that runs ESPHome — if HA can’t reach the device’s API, it likely needs a power cycle. Also useful for monitoring the HA server itself (the watchdog plug is independent and will cycle the HA host if it stops responding).

On boot behavior: Relay cycles off/on at startup (restore_mode: ALWAYS_OFF) to clear any hung state.

Shared Infrastructure

Both configs use a common reusable .network.yaml package providing:

• WiFi with AP fallback + captive portal
• Web server (port 80) with authentication
• Home Assistant API with encryption
• OTA updates
• WiFi signal strength + uptime sensors
• Restart button
• SNTP time sync
• Auto-reboot if WiFi is lost for 15 minutes

The composable package approach (packages: !include) keeps each config DRY — board-specific settings, network config, and watchdog logic are each in their own file.

Hardware

SONOFF S31 — an ESP8266-based smart plug. Flashed with ESPHome via serial (one-time, before sealing the case). Subsequent updates via OTA. Available for ~$10–15.