I believe that is correct. I read recently that all vehicles made after a certian date must have the TPMS installed. The system works off the valve stem somehow.
Here is an article about them.
http://www.aa1car.com/library/tire_monitors.htm
My idea, if I ever get a new car, is to take all the sensors and put them in some kind of container that can be pressurized and sealed to hold the pressure and then install regular valve stems in the rims.
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