Today it happened again. I left my mobile phone at home. I realized that before entering the train, so I went back, grabbed it and went back to catch the next train. This gave me a few minutes to think about that ;-)
You got Android Wear/Watch and already have the smart unlock functionality where your watch (if it is near your phone) can unlock it.
Now you also could detect the opposite scenario, my watch detects it lost the “visibility” of the my mobile phone, so an alarm could pop up on my watch, notifying me about the fact that it left my phone. I can dismiss the alarm, and decide if I go back.
This might cause a few false alarms, but with a small set of additional rules (like “only do this at home/work”, only do this around 8 am and 6 pm) these could be reduced quite a bit.
Please let me know when you are ready.
PS: Actually I do need to buy a watch for that …