Opening your door with bluetooth
This guy did it. How cool is that?
I know him personally, so that's why I know why he did it. The door he opens isn't openable from outside by default so he needs to make a detour to use a normal key-locked door.
Ah, what I wouldn't give to be able to hack that and get it to say "I can' t let you do that Dave" when he tries to get in.