We've got the TST 507, bought it at the Goshen Rally last year. When I installed it, the buttons on the monitor were in the wrong positions, & I had to get some brain cells working to install it. Contacted TST, and they replaced it. Then while we were enroute to Texas this winter, it started chirping, but showed no errors. Stopped & checked the tire in question & no problems. I unplugged it & restarted it & everything was fine...for a while. It did this several times on 3 different tires & still didn't find any problems. Contacted TST again & they replaced EVERYTHING, at no cost. All in all I'm satisfied with the system & the customer service. So far I haven't had any tire problems, knock on wood!