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Tire sensors broadcast a unique number
The sensor measures the tire pressure and sends a radio transmission to the car's central computer. The unique number is how the computer knows which tire to pair with, so the tire repeats it constantly as the car drives down the road, announcing itself as something like Acura tire number 1234567.
Anyone who puts small sensors along a highway can pick that number up as cars pass, and companies have done exactly that. A military that already knows a vehicle's tire sensor number can place a trigger sensor at the end of a certain road, and the sensor cues them when that vehicle drives by.
The number also identifies a car after its license plates have been swapped, because a driver who swaps plates is unlikely to remember to swap the tire pressure sensors. The sensor was carelessly engineered, and it turned into a surveillance device by accident.
Why do cars have tire pressure sensors?
Congress passed the TREAD Act in 2000 after a series of fatal rollover crashes involving underinflated tires. The law directed federal regulators to require a warning system in new passenger vehicles. The National Highway Traffic Safety Administration wrote the rule, and it reached all new light vehicles sold in the United States with the 2008 model year.
How does a tire sensor send its number?
A direct-reading sensor sits inside the wheel and combines a pressure gauge, a battery, and a small radio. Many sensors in North America transmit at 315 megahertz, while European ones commonly use 433.92 megahertz. The sensor sends short bursts, and each burst carries its identification code along with the pressure and temperature readings. The battery is sealed in, and a sensor typically lasts five to ten years.
Why does each sensor need its own code?
The car's receiver hears every nearby transmitter, including those from the cars beside it at a stoplight. A code lets the computer ignore tires that are not its own and tell the front left tire from the rear right. When tires are rotated or replaced, the car must relearn which code belongs to which position. Shops use a handheld tool to read the codes and register them with the car.
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