Schrader Bridgeport is the market leader in direct Tire Pressure Monitoring Systems. Direct TPMS use pressure sensors inside each tire to transmit data to a dashboard display alerting drivers to tire pressure problems.
I'll bet anything you can track cars with them, just as you can track some joggers by their sneakers.
As I said before, the people who are designing these systems are putting "zero thought into security and privacy issues. Unless we enact some sort of broad law requiring companies to add security into these sorts of systems, companies will continue to produce devices that erode our privacy through new technologies. Not on purpose, not because they're evil -- just because it's easier to ignore the externality than to worry about it."
hardware
prices 
