You can add a tile on a dashboard with the Last Updated.
Could RM4 get access to this attribute via the Custom Action.
I would like to periodically check the attribute to make sure the device is still on line.
This stems from having a water sensor go off line and not knowing until I saw there water on the floor and no warning from the sensor.
I'll give it a try. I don't see why it wouldn't work. I thought that I had seen this before but in my searches I somehow jumped the rails and ended finding the App Watchdog.
How would you want this to work? "Last Updated" is more like an attribute (though not technically one--more just part of the device metadata). There's not a command you can run, which is what a custom action would accomplish. It sounds like you would more want it to be usable as a trigger or possibly in a conditional, either way acting as a sort of pseudo-attribute whose value you can read (and do with as you please: compare, wait for it to change, etc.).
That being said, for the purpose I think you're aiming for, I'd just recommend Device Watchdog. 
To use in calculating elapsed time since last update. My research on the topic was a fail and completely my own fault. I have completed install of Device watchdog. It is doing exactly what I needed. Thank you.
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