Hubitat has no built-in mechanism to test whether devices are communicating with the hub. There are community apps that can send a notification based on device activity. I use one from @bertabcd1234, linked to below:
That being said, if your needs are mission critical - as they appear to be, I would recommend using some more robust approach to your automation that isn't dependent on wireless communication from a sensor to a hub.
For instance, I have an inline blower in one of my HVAC ducts. I need this blower to turn on/off in sync with the air-handler/furnace blower. My approach here, which has worked for about a decade, is to wire the blower through a relay. The relay-coil is controlled by direct wiring to a current sensor switch whose CT senses current in the neutral for the air-handler blower.
This system has never failed - it is used approximately 25-30 times a day. Since 2012, the inline blower has turned on and off approximately 100,000 times in synchrony with the main blower without issue. Although, to be fair, I've monitored the state of the inline blower for only the last 6 years - by measuring power consumption.
Given the vagaries of wireless communication, especially with battery-powered devices, I would recommend you use some robust, hard-wired, approach for your application.
