Don Park posts about the idea of a Cellphone Rescue Button.

To use your cellphone to make a Great Escape, just download a piece of yet-to-be-written software and set the delay time (let say 1 minute). To use it, just put your hand into your pocket and press a button. After 1 minute, the phone rings and you say "Excuse me, I have to take this. [after ten seconds] I am sorry, I have to leave, it's an emergency." [Don Park's Daily Habit]

I would love something like this. There haven't had many times I've wanted one, but I can think of a few times it would have come in handy.