Originally Posted by rowan

Kinda related, I'm currently working on a computer for my car which uses an old mobile (cell) phone and GPRS to connect to the internet and phone home regularly. It also has GPS and a video camera pointing out the windscreen. If anyone ever steals it, I'll be able to see their exact location, and what's in front of the car.

(The computer isn't specifically for this situation but as per the OP it will help if it ever does get stolen...)