Spy My Ride: Somebody may be tracking your vehicle and you don't know about it![Tire Pressure]

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[Tarantulas]

Cue the black helicopters. From the original article:

With minor limitations, TPMS can be used for the very purpose of tracking your vehicle in real time with no substantial investments!

From the Subaru information page:

When the vehicle goes 7-20 mph, a roll switch inside the sensor turns on and the sensor starts to take measurements every 30 seconds, and sends the results about once a minute to a receiver module under the carpet by the drver's door. Presumably all four transmitters start squawking at about the same time, which means that your car sends out a recognizable signal once every minute.

If I'm driving 65 mph on the freeway, I cover 5720 feet every minute. If the low power signal can be detected 50 feet away, that's 105.6 sensors every mile, on both sides of the freeway, just to make sure it can detect my car. I would call that a substantial investment.

Also:

TPMS can also be used to measure the speed of your vehicle. Similarly to highway/freeway speed sensors that measure traffic speed, TPMS readers can be installed in pairs to measure how quick your vehicle goes over a predefined distance.

If they were transmitting continuously this would make sense. Since they aren't, it doesn't.

[Flying Circus]

Only the most sophisticated TPMS systems use sensors on the tires- those that report a pressure number. Most cars use data from the anti-lock braking system that activates a idiot light in the dash if the tire is rotating at a different rate than other tires or outside an accepted range.