Like many people today, I have a GPS (Global Positioning System) navigation system mounted semipermanantly in my car to help me get around when I'm out and about. Every once in a while, however, I find myself being asked a rather curious question to which I haven't really put together a rehearsed answer. That question is this: "If you're so consciencious about your privacy, why do you have a GPS unit in your car? Aren't you worried that you'll be tracked wherever you go by your GPS?"
The short and simple answer to that question is, "No, I'm not concerned about that," and here's why:
GPS nav systems, like my TomTom, are basically small computers that contain databases of maps and roads coupled to a high-frequency radio receiver that picks up transmissions from the GPS satellite constellation. The GPS performs a lot of very specialized math using the information carried by the signals to figure out where on the planet it is. This is all well and good but that doesn't help Them locate me because They have no idea where my car is at any particular time unless They happen to be looking right at it. To do so, a GPS unit would need to have a transmitter inside of it to broadcast its current location on a certain frequency. For various reasons (including the sheer number of GPS units on the road, power requirements, hardware hackers opening their GPSes up to play with them and blowing the whistle, and FCC regulations) this simply isn't done in consumer GPS units (though specialized surveillance devices are available on the grey market, such as the Quick Track Pro and various devices sold by Laipac Tech). On top of all of this, The Powers That Be simply don't have enough people to keep an eye on the movements of several million vehicles simultaneously - when you stop and think about it, it's kind of ludicrous.
In short, unless you've gotten on the bad side of a governmental agency, a law enforcement agency, or a technically knowledgable private investigator, you really don't have anything to worry about. Now, there are some on-board nav systems like OnStar which do report your position to a central office, but a GPS unit that you can purchase at the corner consumer electronics store doesn't have this sort of functionality - not only would you have to subscribe to such a service to make it worth their while to keep an eye on you (paying the salary of an eye in the sky, as it were), but such devices draw a lot more power than you might think and would run down faster, something that a consumer would no doubt take notice of at the worst possible moment.