I think an app on your phone is a better way, if the phone has not moved in the last 24 hours or whatever, then an email could be sent. Something like that.
You can reset the switch in any way you like, I was playing around with emailing through single-use codes and port knocking and so on. One I never got around to trying is a basic phone check: You have a cron job that scans all bluetooth devices within range and checks for your phone's MAC address. If it's there, it resets the timer. If you're out of physical range (or turn off your bluetooth) for too long, it triggers the switch.
Not quite what you described but it does perform some of the same function.
