GPS Tracking for Stolen Bikes

I think this is the best way to go. Do this to a cheap, small mobile. Take it apart, wrap it in a condom, stuff it down the seat tube (I'm sure you can get reception inside a seat tube). Without the backlit screen and the speaker, the battery might last for weeks. When it does need to be recharged, take it out and plug it in, just like you would a normally. Especially if you can get it on a 'standby' mode.

Hmm, wouldn't the tube act as a Faraday cage?