SDR Listens In To Your Tires

Jun 13, 2023

[Ross] has a 2008 Toyota Tacoma. Like many late model cars, each tire contains a direct tire pressure monitoring sensor or TPMS that wirelessly sends data about the tire status to the car. However, unlike some cars, the system has exactly one notification to the driver: one of your tires is low. It doesn't tell you which one. Sure, you can check each tire, but [Ross] had a different problem. One sensor was bad and he had no way to know which one it was. He didn't have any equipment to test the sensor, but he did have an RTL-SDR dongle and some know-how to figure out how to listen in on the sensors.

The key was to use some software called RTL-433 that is made to pick up these kinds of signals. It is available for Linux, Windows, or Mac, and supports hundreds of wireless sensors ranging from X10 RF to KlikAanKlikUit wireless switches.

The program successfully found three of the TPMS sensors and helpfully decoded the information they were sending. It seems the bad sensor was totally dead. Since the transmitters are extremely low-power, it was easy to move the antenna close to each sensor to identify which one was not transmitting. We aren't sure if the transmitter was dead, or if it was just unable to send proper packets. If it was actually dead, a field strength meter might have found it. However, at such low power levels, the method [Ross] used might have been easier.

Besides, you probably have an RTL-SDR hanging around and are less likely to have a field strength meter. Not that you couldn't make one with a germanium diode and a sensitive voltmeter, but still.

We’ve always been impressed with the homemade TPMS we’ve seen. We’ve also seen RTL-433 adapted to read medical devices.