Andrew Leinonen created the ultimate deterrent to bicycle theft -- a lock that's integrated into the bicycle's frame. He calls his invention the StayLocked Bike.
The concept is simple, but brilliant. Instead of external lock that can be cut without damaging the bike, Leinonen's lock is integrated into the seat stays, an integral portion of the frame that connects the rear forks to the main tube that holds up the seat.
To steal the StayLocked bike, a thief would have to cut these seat stays. It wouldn't take too him long to figure out he stole the wrong bike. As soon as he hopped on the bike, it would buckle under his weight and he would go crashing to the ground. [Wired]