Bottom line, anyone with $50 ($40 for the device, $10 for a pre-pay SIM card) and who can pop your hood and work for a few minutes can monitor everywhere your car goes. He can also kill your ignition remotely, but that would be a dumb thing to do because it would most likely lead to you finding the device.
Oh, sure, it’s sold as a way to keep track of your own car, but it’s important to think about how a technology (or a law) can be misused.
On the other hand, Big Brother already has a real good idea where your car goes, between OnStar, your highway toll transponders, the RF transmitters in your tires, always-on license plate cameras, and probably other things I’m forgetting, you must assume your car’s location is always known in any urban area. Roll in constant tracking of your cell phone’s location and goverment access without warrants and Big Brother knows where you are pretty much all day every day. And don’t forget listening in whenever
they get a warrant they want to. (What? Don’t carry a cell phone? But I neeeeeeeeed it!) (It used to be considered good advice to the paranoid to take the battery out of the phone if you weren’t using it. That advice is obsolete.)