Tyre Pressure Monitor - where are they?

[xxx_mojo_xxx]

I recently had my tyres replaced and was intrigued to find there were no tyre pressure sensors inside the rims. 

My previous car had a bit inside each wheel behind the valves which I was told were the pressure sensors. 

The question is where are the tyre pressure sensors on the Golf?  Is there one for each wheel?

I know its working, because I had to reset the sensor a couple of miles down the road after having the tyre pressure slightly dropped in the new tyres.

[Poppa Dom]

The TPS system work on the basis on rolling diameter of wheels and wheel speeds rather than pressure sensors.

[stealthwolf]

+1.

My tyre pressures were okay for a few weeks. Then suddenly the light came on and though three had dropped a little, one had dropped to around 2.0 bar from 2.6 (29psi down from 37psi).