I have the Tire Minder A1 system. It works quite well. It came with the cap type sensors and a repeater. It will report when a sensor loses connection and will reconnect if the sensor comes back. Minder Research has a free battery replacement program. You just pay $5.00 shipping and they will mail you as many batteries as you need along with the rubber o-rings to seal the caps.
I went with the metal valve stems on the MH but still have the rubber ones on the toad as they are really short and the sensors actually touch the rims. Will have metal valve stems put in next year when I replace the toad tires. So far, no leaks.
EDIT: They also come with locking nuts that require a wrench to remove. I have the locking nuts on the MH but not the toad as the stems are too short. In 3 years, never had a sensor stolen off the toad.