My dealer told me that the sensors are in the valve stems. Gave me an
estimate of $60 each, for my snow tire rims. Thanks, but No Thanks.
I guess I'll wait until spring, to see how the system works.
By-the-way, for those of you who are experiencing pressure fluctuations
between a cold tire and a warmed-up one, try filling your tires using Nitrogen.
The pressure does not change with a change in temperature.