If you carry a cell phone while on, remote tracking is possible too. It's even easier since usually the wireless signal is better than the multiple satellite signals that need to reach the gps under (or wherever they put it) the car and might even be more precise in city environments due to the closer spacing of cell towers.

I find it odd that people are so concerned about this while they carry a tracking device with their person all or most of the time...

EDIT: not only that, can be instructed as a real time listening device, if you are that paranoid :)

I believe the context we were talking about was for GPS devices.

I'm not disputing the use case of tracking via cell phone but that's a whole other ball of wax.