Klaus,

The display shows the actual tire pressure and the temperature. You can cycle through the 4 tires and even the spare (if you purchase an extra sensor).

I belive you also get an audible alarm if the pressure drops more than 25%. The unit I originally had you could program the alarm to different percent drops in pressure, but I don't know about the replacement one as I can't find the installation manuel on line, so will have to wait to get the actual one.

Installation seems pretty straight forward to hard wire it. Attaches to a constant and switched power source. The display is small enough to fit most places. I'll be mounting on the center counsel at the bottom through one of the plugs for a missing option. I've also seen a "third eye" system that had a pretty slick mount on the rearview mirror.

Not sure what someone would charge you to install. I'd guess they would mount the sensors for free if you purchase the system from them. Otherwise the cost would be like fixing a flat since you have to un-mount and remount the tire along with balancing. This also might be free if you are replacing the tires at the same time.

Jerry