[nobodyshere]

Doesn't really seem that difficult. The patterns of picking up a phone, running with it and having it just lay on a vibrating surface are very different. It would be particularly easy to spot panic during a usual running routine.

[taeric]

More, I'd imagine you could look for a signal common to many devices. Unless you are picking up all phones in your household with the same signal, any signal common to them all is likely more global. Could detect if folks are in the same car?

[lm28469]

> Doesn't really seem that difficult

Companies lose billions on projects every year because someone uttered these exact same words.