ORIGINAL: epegasus
These things work wirelessly, right? Can they receive signals from other people's cars? I mean, in traffic your receiver can be closer to a neighboring car's tire than it is to your own rear tires if the receiver is positioned under the dash. Or, are they keyed specifically to the transmitters in just your car. That seems unlikely though with the limited number of frequencies available. All moot if the system isn't wireless, though.
The system IS wireless. The TPMS sensor is attached to the base of the valve stem. It sends an RF signal to report pressure. When the sensors are first installed (and when they are replaced) the sensors are activated and the computer is programmed to recognize the sensor ID. This is the part that keeps it from reading another car's signal as you are driving alongside. On a system that displays each tire's location and pressure individually, you need to reprogram each time the tires are rotated. For systems that simply set a generic warning light and not position/pressure, you do not have to reprogram after a rotation.