I have read that some see their TPMS reading a few pounds less than their tire gauge. So I did the most simple test. I filled my tires to exactly the spec for my car, very carefully, with what I think is an accurate gauge (according to tons of Amazon reviews...). 38 front, 40 rear. I then drove just far enough to get the sensors to report (less than 1/4 mi) on a very cool day with no sun on the road and slowly. They gave the exact same reading as my gauge. I was actually quite surprised. However, when I bled my tires dry in order to put AlloyGators on, the alarm did not go off until they were essentially completely flat. So I don't trust their ability to warn me that I am low, only that I am flat, which is WAAAAY too late. What's up with that? My '06 Acura would warn after a 10% drop in pressure. So I check the widget regularly. I will say that the tires don't seem to lose pressure except when the temp changes significantly. I expected that they would.