One of the more interesting ways to stop a bike thief comes from liseman, who rigged a mobile phone to a stun gun hidden in the bikes water bottle cage. When the phone is called it activates the stun gun.
This dude creeps me out a little.
My question is would the rider actually get shocked? Rubber grips, soles, and seat might insulate the rider from the charged bike frame. You might have to run a copper wire up the seat post onto the seat. That'll give em the ole "how's your father" right in the coin purse!
Thanks to Shryke for the link.