How do tire presure sensors work?

Uhhhh....I don't know.....good question.

There is a small computer chip with an air pressure sensor attached to the inside of the rim. When the air pressure gets too low, it sends a signal to the onboard computer. I know Indy race cars have been using this for quite some time.

Each sensor emits a different digital radio signal to an antennia. Lithium Ion battery good for five years as the sensor spins the signal starts 19 mph or so. The car body control module reconizes the sensor as being less than 29 psi and turns on the light. Many Nissan cars have had the system from 2002 year model. We all can thank Firestone and Ford for one more thing that can turn on a dash light. Not really a bad idea because one out of three cars have at least one tire low on air. Custom rims and tires can be a problem the sensor has to be aimed right. So the sender antennia to brodcast it's signal to the BCM's antennia.

I suspect it is a radio-frequency connection. A direct connection is possible. Like the track and wiper system used on the contacts for horn, cruise control etc. in the steering wheel. Seems like the super car Porsche 959 had a continuous connection to the tire pressure for topping-off with air on an ongoing basis. Have also heard the same thing about military Hummers. This would involve the use of dynamic seals similar to pump impeller seals.

some systems use a sensor installed on the rim,other systems use the ABS wheel sensor to monitor the speed of each wheel,the difference in wheel speed changes when the air pressure drops.making one wheel turn slower than another.

Give the 10 pts to John Paul. They work off of a RF transmitter mounted in each wheel. I don't know about the 300, but they are either stuck to the inside of the rim or sometimes attached to the valve stem. Very handy, but they make changing a tire a pain in the a$$. They are very fragile and cause balance problems.

There are two types of sensors - direct and indirect. Direct sensors actually measure the air pressure using a sensor attached to the inside of the wheel and report back to your dashboard using wireless technology like a cordless phone or bluetooth. These are the best systems. Indirect systems use the ABS braking system so determine if one tire is rotating more rapidly than the others. Of course, if all four tires were underinflated it wouldn't warn you. These systems only exist because they are cheaper than direct systems. Car companies love 'em, tire companies hate 'em. Since it sounds like your vehicle was parked, I'm guessing that you have a direct system.