Monitor if entity is changed, set alert if not changed within a time period

[123 (Taras)]

Fedot’s solution is basically what I have suggested to others but using datetime objects in the subtraction instead of timestamps (slightly more compact template).

  {{ now() - states.input_number.test_number.last_changed > timedelta(hours=1) }}

What you might be thinking of is this automation that periodically checks for stale sensors.

Polling Devices to Avoid Silent Failure

Paste this template into the Template Editor. It will list all sensors whose states have not changed in the past hour (3600 seconds, change it to whatever duration you prefer). {{ states.sensor | selectattr('last_changed', 'lt', now()-timedelta(seconds=3600)) | map(attribute='entity_id') | join(', ') }} You can use that as a starting point to create a template that checks for ‘stale’ entities. If you want it to check sensors and binary_sensors, use expand(). {{ expand(states.sensor, …

The requirement was to check every 4 hours for any sensor or binary_sensor that hasn’t been updated in several hours. It uses a Time Pattern Trigger in order to control the polling interval (to avoid checking every minute as in a template employing now()). It can be easily adapted to check every few minutes and could be made to check on startup as well (add the appropriate homeassistant startup trigger).