Tire Pressure Monitoring Systems & Privacy

Via HexView -

There is no shortage of articles discussing privacy issues introduced by new technologies. ReadID, passports, chips in currency bills, and other engineering marvels designed for purposes of tracking and monitoring, always come with a bouquet of questions and privacy concerns. On the other hand, technologies not specifically designed for monitoring can sometimes be used for this very purpose and privacy problems introduced by them are often overlooked. Tire Pressure Monitoring Systems (TPMS) is one of those technologies.

TPMS lets on-board vehicle computers measure air pressure in the tires. If you purchased a new vehicle in the last 2 years, it is very likely that it came with TPMS. If you live in the Unites States, your next vehicle will contain TPMS whether you like or not -- in April 2005, National Highway Traffic Safety Administration issued a rule requiring automakers to install TPMS sensors in all new passenger cars and trucks starting in September 2007.

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In a typical TPMS, each wheel of the vehicle contains a device (TPMS sensor) - usually attached to the inflation valve - that measures air pressure and, optionally, temperature, vehicle state (moving or not), and the health of the sensor's battery. Each sensor transmits this information (either periodically or upon request) to the on-board computer in the vehicle. To differentiate between its own wheels and wheels of the vehicle in the next lane, each TPMS sensor contains a unique id. The receiver is "paired" to the sensors very much as a Bluetooth device. The vast majority of TPMS sensors transmit information in clear text using one of the assigned radio frequencies (typically, 315MHz or 433MHz).

Here is where privacy problems become obvious: Each wheel of the vehicle transmits a unique ID, easily readable using off-the-shelf receiver. Although the transmitter’s power is very low, the signal is still readable from a fair distance using a good directional antenna.

Remember the paper that discussed how Bluetooth radios in cell phones can be used to track their owners? The problem with TPMS is incomparably bigger, because the lifespan of a typical cell phone is around 2 years and you can turn the Bluetooth radio off in most of them. On the contrary, TPMS cannot be turned off. It comes with a built-in battery that lasts 7 to 10 years, and the battery-less TPMS sensors are ready to hit the market in 2010. It does not matter how long you own the vehicle – transportation authorities keep up-to-date information about vehicle ownership.