Of course if the penalty for tampering with it is ten years in a "Federal pound-me-in-the-*** prison," the instances of tampering would probably be fairly low.
And they'd know if you tampered with it by having police vehicles scan your system while driving in traffic much like the IFF transponders used in military aircraft.
Yes, I prefer having my plane squawk my location too - it keeps me on the ATCs screens and out of the windscreen of something much larger and faster. But on the road, where I go and how I get there is MY business, not the gov'ts.
To hell with trying to tamper with a system like this - that's treating a symptom. I'd rather treat the disease at that point: Vote from the rooftops and get rid of a government that was that heavily involved in my daily life.
Guess I won't be buying any new cars after 2010.