Me too. Especially of it were a factory installed option. You could probably encapsulate the electronics in one of the frame tubes, which would mean it would be welded in to the bike. Impossible to detect casually, and nearly impossible to easily defeat without destroying the bike itself.

Given the ratio of hours ridden to power draw of a small tattletale device, you could probably put a couple of magnets on the crank assembly (inside the tube the connects the crank to the frame), along with a couple hundred coils of wire and create a very nice charging circuit. It might take even 100 hours of riding to build up an initial charge, but I'm guessing that would be no problem in a typical scenario, even if it took 2 weeks to get there.

For a reason I can't reply to you brk but I used the same ideas.

My last question was about communicating openly or not about it.

    - Openly would make robber aware and probably come up with attacks 
      or blocking means, but that would surely render their activities 
      a lot more complicated. Could be mass-produced.

    - Secretly a few people would have it and use it as bait, and 
      authorities being aware of the scheme would casually catch robbers 
      later. No mass-production

Oh one more thing, I was thinking about using a cellular module with custom firmware to reply to text messages with gps position but I'm not sure it's feasible.