One automation to watch every battery sensor in the house

The problem with battery-powered sensors is you forget they have batteries — until one dies silently and you notice a week later that a door or motion sensor stopped reporting. This is a single automation that checks them all, once a day, and only bothers me when there’s something to act on.

The design#

Every day at 12:30pm it loops over my battery sensors, and if any is below 30% it announces which one(s) — on Alexa and Telegram. If everything’s healthy, it stays silent. No daily “all batteries fine” nag.

- id: battery_low_daily_check
  alias: 'Battery: daily low check'
  triggers:
  - platform: time
    at: '12:30:00'
  variables:
    threshold: 30
    sensors:
      Door sensor: sensor.door_battery
      Inside motion: sensor.inside_motion_battery
      Outside motion: sensor.outside_motion_battery
    low: >-
      {% set ns = namespace(items=[]) %}
      {% for name, eid in sensors.items() %}
        {% set v = states(eid) %}
        {% if v not in ['unknown','unavailable','none', None] and (v | float(101)) < threshold %}
          {% set ns.items = ns.items + [name ~ ' at ' ~ (v | float | round) ~ ' percent'] %}
        {% endif %}
      {% endfor %}
      {{ ns.items | join(', ') }}
  conditions:
  - condition: template
    value_template: '{{ low | length > 0 }}'
  actions:
  - data:
      message: 'Low battery warning. {{ low }}.'
      data:
        type: tts
    action: notify.alexa_media_echo
  - data:
      message: '🔋 Low battery: {{ low }}.'
    action: rest_command.telegram_notify
  mode: single

The details that matter#

It skips glitch readings. Cheap battery gauges occasionally report unavailable or unknown, or briefly spike to a wrong value. The template explicitly filters those out (v not in ['unknown','unavailable','none', None]) so I don’t get a false “0 percent!” alarm during a momentary dropout.

It names the culprit. Instead of a vague “a battery is low,” it says exactly which sensor and its level — “Door sensor at 25 percent” — so I know what to grab a battery for.

A once-a-day snapshot is naturally glitch-proof. I considered making it event-driven (fire the instant a battery drops below 30%), but that’s fragile — battery readings are noisy and would false-trigger. A daily check at a fixed time is immune to momentary noise: worst case it catches a bad reading one day and is fine the next.

Telegram + a real-world gotcha#

The alert mirrors to Telegram via a rest_command that hits the Bot API directly. Worth noting: my home ISP intermittently blocks api.telegram.org. When that happens the REST call just fails silently (Home Assistant’s rest_command is continue_on_error by default) and the Alexa announcement still works — then Telegram resumes on its own when the block lifts. Graceful degradation for free.

Takeaway#

The trick isn’t the code — it’s the restraint: only speak when there’s something to do. An automation that announces good news every day gets ignored (or disabled). One that stays quiet until it matters is one you actually trust.