Thanks Junkyard!
Few flaws with that logic. A cycle computer is basically little more than a digital watch, so it can run on a button battery for years and years.
Whereas a tracker would have very different power requirements. Even in a sleep state it would still need to regularly connect to some kind of network to see if it needed to wake up, so would need a transceiver, antenna and enough power to connect to the nearest cell tower.
State of the art commercial units looks like this:
[video]http://www.youtube.com/watch?v=ICb4g0fcBqY[/video]
http://traqm.com/eye-trac-911-personal-tracker/
And the battery lasts for “up to” 40 days.
Still possible, but hard to conceal on a bike and would require regular recharging.