I'm monitoring 4 contact sensors to control a relay. If any or all of the 4 contact sensors are open the output relay will be open. When all 4 contact sensors are closed the relay will be closed.
My question is about exception handling when a contact sensor battery dies or stops communicating. Ideally I want the rules to ignore the dead contact sensor and continue with the remain three working sensors.
I was hoping to use conditional rules, but I didn't see a condition for "no communication", or "indeterminant" .
Is there perhaps a different way to achieve the same result? How does the Hubitat normally handle sensors that are offline? The system must never keep the relay open due to a dead or non-communicating sensor.
If the sensor dies in the closed position then it shouldn't matter for your use case since you only care if any sensor is open. The sensor should remain showing the last state before the battery died. If you required all sensors to be open, that would be a different story.
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.
Thank-you, do you know if the system will always report the last known state of a device before it lost communication? If it was open it will continue to report open, and if it was closed it will continue to report closed?
