Uber-geek shop
Maplin sell car locaters. When you leave your car in an airport car park or shopping mall you point the key fob at the vehicle and press a button. When you return from holiday or whatever the fob will guide you to your car. It's at the rudimentary stage at the moment, range is 180 metres and it won't work with buildings in the way, but I can see small devices fitted inside a bike frame that would enable you to track down the stolen bike's location to within a few feet, so you can torture the thief to death with pliers.
I mean call the authorities.