There are many possible solutions, the one I like (and use) is this: [[RELEASE] iPhone WiFi Presence Sensor
For me it is 100% reliable and will quickly report you are no longer present since it has a very short range. The range is so short that it doesn't always pick up my presence while I am walking up to my door (if your phone is operating on 2.4 ghz wi-fi as opposed to 5 ghz wi-fi you will get better range). So I just program my alarm to dis-arm when the correct unlock code is entered in the door's keypad. You could always use the Hubitat app's geofence as well if you want auto unlock and auto disarm when you arrive home (I am sure someone will be able to help you get it working).
For the Google Home integration, I would just make a virtual switch (Call it "House Alarm"). Make a simple rule that when the switch turns on HSM is armed-away and when the switch turns off HSM is disarmed. Then just tell google to turn on or off the switch. You could also create a dashboard for the Hubitat app that does all of this as well. Or you could put a tablet on wall at your entrance to run a dashboard that does all of this as well.
I can currently Arm my Arm-Away from: a dashboard on a tablet at my entrance, a dashboard on my phone.
I can currently Disarm my Alarm from: a dashboard on a tablet at my entrance, a dashboard on my phone, a correct code being entered to unlock my door, wi-fi presence sensor (also auto unlocks the door), Hubitat's geofence (also auto unlocks the door).
