How to look for devices that are no longer sending data

I have some blue tooth temp sensors that report back to a esphome esp32. Can someone provide some direction on how you could raise an alarm (via automation perhaps) if there is no data received from any of those sensors in some period of time - say an hour. It would also solve the problem if the esphome board got unplugged or failed. Having my freezers temp monitored is useful - but I need someway to verify that data is being received. Thanks for any breadcrumbs!..

That way if the state doesn’t change in 1 hour, the automation will run

alias: teste
description: ""
  - platform: state
      - light.entrada
      hours: 1
      minutes: 0
      seconds: 0
condition: []
action: []
mode: single

Maybe there’s a better way.