I'm currently using the GSM-GPRS-GPS Tracker and it is been installed in the bike:
Rest of the parts in an undisclosed position, tracker is long life battery powered but for obvious reasons have established a battery connection not very visible of course.
The reason for this installation is to provide me enough time to track bike is case someone decides to take it as a souvenir (joke),
Being a PI using such devices to track cars and vehicles generally in cases like adultery etc with very satisfactory results.
Furthermore in a late Police seminar the constables from vehicle theft department described the procedure after a vehicle stolen as such: thieves remove vehicle, park it in a suburb away from original crime scene, arrange surveillance for vehicle usually for up to three days in order to establish in vehicle is equipped with a tracking device, if not then remove vehicle for transform in used parts or transfer it to another country lately they prefer African ones. In those three days when the owner has installed a tracking device then by submitting to Police tracking details they have a pretty good change to recover it.