Most Direct TPMS (Tire Pressure Monitoring Systems) deploy tire pressure sensors on each wheel of a vehicle. As tire pressure data is collected for each tire, it is sent to one or more TPMS receivers, using RF (radio frequency) technology.
The majority of Direct TPMS installations transmit their data via UHF (Ultra High Frequency) radio. TPMS data is typically transmitted in one of two frequency ranges, which depends on the geographical location of the TPMS. TPMS signals are transmitted at about 433MHz in Europe, and at 315MHz in most other parts of the world.
Additional information such as the TPMS serial number, is also transmitted to the TPMS receiver(s), acting as a unique identifier. The inclusion of TPMS serial number information in the TPMS data transmission prevents a vehicle's TPMS receiver(s) from capturing tire pressure monitoring data from another TPMS equipped vehicle that is nearby.
UHF based TPMS data transmissions occur in the unlicensed ISM radio band range. The ISM radio band is primarily reserved for industrial, scientific and medical use. Nevertheless, some devices, such as non-industrial microwave ovens, also utilize the ISM radio band.
A number of other non-industrial devices such as cordless phones, Bluetooth devices, wireless computer networks and NFC (near field communication) devices now commonly transmit data in the ISM radio band range. In some cases, devices in the preceding list may cause a temporary loss of a TPMS signal, when operated in close range of a TPMS receiver.