Thinking about it... you don't really need a mobile app for presence. As long as your mobile device is joined to your house WiFi, then it strikes me that a pretty simple Hubitat app could periodically do an arp lookup for the phone's MAC addres and a quick ping to establish if the device is currently on the network at the moment. It's not sophisticated, but providing you've got WiFi coverage to the extremities of your house, I don't see why that wouldn't work.
I've just finished work for the Christmas holidays, so I might have a quick bash at that in the next few days, if it turns out my groovy is up to it 
-- Jules
