[syhprum (OP)]

Do they have internal pressure gauges and "Bluetooth" transmitters?

[CliffordK]

It looks like tire pressure monitoring systems are now being mandated on all new cars.  Many of the retrofitting systems are apparently little battery powered radio transmitters that fit into the valve stems.

It doesn't say the frequency.

Ahh, here's another Wikipedia article indicating that at least the passenger car tire pressure monitoring systems run with UHF at about 315 MHZ or 434 MHZ.  Each wheel gets a unique signal identifier (digital?). 

Bluetooth apparently runs in the ISM band from 2400–2480 MHz

It sounds like these pressure sensors are battery powered.  I wonder how long until they design an automatic recharging system somewhat like some high-end watches.

How long do the batteries last?  Can they be changed without removing the tire?
Hmmm, in a wise move, replacing the batteries requires replacing the entire sensor unit at about $40 each, I think, plus labor. 

It would seem like they could make a ring shaped user replaceable battery that would fit over the valve stem.

Hopefully there will be a manual that explains to a consumer what to do when changing snow tires and road tires.  And, I assume the racers have a method to update the sensors in the 10 seconds it takes to change a tire during a race.

[syhprum (OP)]

I am sure their would be heads to roll if the wheel changing crew at a F1 event took 10 seconds, the wheels are normally changed and the car away in 3 !
Thanks for the information.