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WSDCGQ12LM sensors report battery: 0 due to firmware quirk. Override battery calculation using voltage via homeassistant value_template. Also adds zigbee_sensor_stale alert for detecting dead sensors regardless of battery reporting accuracy (1 hour threshold). Device configuration moved from external devices.yaml to inline NixOS config for declarative management. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
64 lines
2.9 KiB
Markdown
64 lines
2.9 KiB
Markdown
# Zigbee Sensor Battery Monitoring
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## Problem
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Three Aqara Zigbee temperature sensors report `battery: 0` in their MQTT payload, making the `hass_sensor_battery_percent` Prometheus metric useless for battery monitoring on these devices.
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Affected sensors:
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- **Temp Living Room** (`0x54ef441000a54d3c`) — WSDCGQ12LM
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- **Temp Office** (`0x54ef441000a547bd`) — WSDCGQ12LM
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- **temp_server** (`0x54ef441000a564b6`) — WSDCGQ12LM
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The **Temp Bedroom** sensor (`0x00124b0025495463`) is a SONOFF SNZB-02 and reports battery correctly.
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## Findings
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- All three sensors are actively reporting temperature, humidity, and pressure data — they are not dead.
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- The Zigbee2MQTT payload includes a `voltage` field (e.g., `2707` = 2.707V), which indicates healthy battery levels (~40-60% for a CR2032 coin cell).
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- CR2032 voltage reference: ~3.0V fresh, ~2.7V mid-life, ~2.1V dead.
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- The `voltage` field is not exposed as a Prometheus metric — it exists only in the MQTT payload.
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- This is a known firmware quirk with some Aqara WSDCGQ12LM sensors that always report 0% battery.
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## Implementation
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### Solution 1: Calculate battery from voltage in Zigbee2MQTT (Implemented)
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Override the Home Assistant battery entity's `value_template` in Zigbee2MQTT device configuration to calculate battery percentage from voltage.
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**Formula:** `(voltage - 2100) / 9` (maps 2100-3000mV to 0-100%)
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**Changes in `services/home-assistant/default.nix`:**
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- Device configuration moved from external `devices.yaml` to inline NixOS config
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- Three affected sensors have `homeassistant.sensor_battery.value_template` override
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**Expected battery values based on current voltages:**
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| Sensor | Voltage | Expected Battery |
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|--------|---------|------------------|
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| Temp Living Room | 2710 mV | ~68% |
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| Temp Office | 2658 mV | ~62% |
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| temp_server | 2765 mV | ~74% |
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### Solution 2: Alert on sensor staleness (Implemented)
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Added Prometheus alert `zigbee_sensor_stale` in `services/monitoring/rules.yml` that fires when a Zigbee temperature sensor hasn't updated in over 1 hour. This provides defense-in-depth for detecting dead sensors regardless of battery reporting accuracy.
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**Alert details:**
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- Expression: `(time() - hass_last_updated_time_seconds{entity=~"sensor\\.(0x[0-9a-f]+|temp_server)_temperature"}) > 3600`
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- Severity: warning
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- For: 5m
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## Post-Deployment Steps
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After deploying to ha1:
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1. Restart zigbee2mqtt service (automatic on NixOS rebuild)
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2. In Home Assistant, the battery entities may need to be re-discovered:
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- Go to Settings → Devices & Services → MQTT
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- The new `value_template` should take effect after entity re-discovery
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- If not, try disabling and re-enabling the battery entities
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## Notes
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- Device configuration is now declarative in NixOS. Future device additions via Zigbee2MQTT frontend will need to be added to the NixOS config to persist.
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- The `devices.yaml` file on ha1 will be overwritten on service start but can be removed after confirming the new config works.
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