Well, I did it, got the Tire-SafeGuard system. I had to get 2 new tires, so had the internal sensors installed on all wheels. Don't have the antennas permanantly mounted yet, but just laying them on the floor all the sensors are picked up fine. I chose this system because they seemed to have the best design. Your choice of internal sensors or external sensors, and unlike Doran external sensors, the Tire-SafeGuard external sensors do report (ambiant) temperature and more importantly, you can add air without removing the sensor. The best place I found to get this was from a guy (timebo) on ebay. I'll let you all know how it performs on my next trip.