I've used the Doran pressure Pro TPMS for over 5 years. Works great and has notified me a few times on low air pressure. I'm sure this saved me a major blow-out. I use them on all 10 wheels of my motorhome and toad.
These are the external sensors that replace the valve caps. So far, they've never been stolen. Other systems may be slightly better, but are also much more expensive. 5 years old and haven't had to replace one yet. I expect the batteries to start going out soon. Then it's $50 each to replace them. End users can't change batteries.
Don't make the same mistake I originally made. I wired the receiver to always be "on". In the middle of the night, the air temperature drops causing the air pressure to also drop. Didn't like the TPMS alarm going off in the middle of the night! I now have it wired to only be on when the ignition switch is on.
