Schrader Electronics, which supplies the major auto manufacturers with the Smart Valve RF Tire Pressure Monitoring System, utilizes such technology. Its sensor is actually part of the valve stem and is accurate down to two percent. The newest versions are utilizing microchip technology, so each TPMS can be extremely small and relatively inexpensive. Phillips Semiconductors has designed a $3 microchip that will communicate with the keyless-entry receiver so the only hardware needed to bring a new vehicle into the world of TPMS is a sensor in the tire.
Intellivalve
Indirect TPMS
Indirect TPMS does not measure actual tire pressure. Instead, it monitors the rotational speed of the individual wheels and calculates that data to warn a driver of tire pressures below the acceptable margin. When a tire loses air pressure its effective diameter gets smaller and the rotational speed increases in relation to the other tires. The vehicle's onboard computer and/or a chip in the indirect TPMS device(s) picks up on the differences in wheel speeds and provides a signal to warn the driver.
Some of these indirect systems tie in directly to the vehicle's anti-lock braking system (ABS), significantly reducing the cost of implementing TPMS.
Most experts say the indirect method is less precise than measuring actual tire pressures, but it's still an effective warning system and is actually in place on a lot of today's vehicles, mostly cars. In fact, there are now more than 2.5 million GM cars equipped with one variety or another of TPMS.
The point to all of this? Keep a close eye on those tire pressures, with or without the use of a TPMS, and you'll likely experience far fewer problems than a truck owner who ignores his rolling rubber.