The SpyLamp looks like an ordinary LED rear light. Inside though, is GPS technology. It works using a pay-as-you-go mobile phone SIM card and a motion sensor. The stolen bike can then be tracked online using Google Maps.
It costs £125, though it will also require the occasional top up of the pay-as-you-go SIM card.
The problem I can forsee though is that a thief may lose the light or sell it to someone else for a small financial gain. Perhaps they designers have antisipated this as they are about to launch a version that can be hidden inside the seat post or bicycle frame.