In February, the Seventh Circuit of the US Court of Appeals ruled in the case of two police officers who had quietly slipped a GPS tracker into the car of a "suspicious" man. The man sued under the Fourth Amendment (unreasonable searches and seizures). He lost. Interestingly, the government conceded that wholesale warrantless monitoring of all US automobiles would be a "different" matter. Different in what sense, I do not know. (I admit that I didn't read the opinion.)
Okay, everybody stay calm. It's just one case, and it may go to the Supreme Court, which may reverse the decision. Or not.
But, really, who cares? As a practical matter, we're headed for wholesale car monitoring already. Open road tolling systems, for example, note the passage of cars, sometimes by RFID, sometimes by license plate imaging. If dynamic road pricing schemes become popular, that'll be another trace you'll leave. And, of course, plate numbers can be noticed and parsed by outdoor video surveillance systems, which are expanding by leaps and bounds. So maybe the court's decision shouldn't bother us unduly, and maybe what the government meant by wholesale car monitoring being "different" was "achieved with zero resistance from the general public."