Tire pressure monitoring systems (TPMS) have been made mandatory on new cars in the US since 2008 by the Tread Act. Most manufacturers field their own systems, but all work in a similar fashion. Early systems had an Electronic Control Unit in the car dedicated to the sensors, receivers spread around the wheel wells, and a transmitting sensor in the tire that takes the place of the tire valve. Almost all manufacturers have ditched the separate receivers and have put them in the ecu itself.
The tire sensor itself houses a microprocessor and enough memory to store tire pressure, temperature and rotation direction values. There is also a radio frequency transmitter and an inertial unit that helps with power management. The sensor doesn’t transmit anything until the car reaches 15 to 20 miles an hour, conserving energy as the built in 3V coin style battery is not replaceable, but is designed to last 10 years… some make it that long, some do not.
Some sensors have to have their electronic id programmed into the car when changed out, some are learned automatically. They have to be dealt with when new tires are installed, typically replacing the seals, but if corrosion has set in, it will probably need a sensor. Learning a new sensor is not usually done by DIY’ers, as the electronic equipment is quite expensive.
Replacing sensors with manufacturers original parts is pretty expensive, rarely costing less than a hundred bucks for a sensor… but some aftermarket types, like VDO’s RediSensor, has stuffed several manufacturers programming into a single sensor, enabling it to replace them directly and be programmed with factory tools. The best thing is that they are available for $35-$50, saving a lot of the cost on new sensors. It is important to use a brand that you trust, as some overseas knockoffs are just too cheap.