How accuracte are the tire pressure monitors?
 

I filled my tires and measured the tire pressure with a new Harley Davidson tire guage. The tire pressure monitors showed different pressures between 1 and 3 psi. WHen filling your tires do you trust the built in guages or a standard old fasion tire pressure guage?

You should buy a good digital gauge, and trust it. They cost about $14.

Depends on the actual system.

One type works of the ABS system. If it notices a wheel rotating at different speeds, it will trigger. So. If all tires are equal, but say, 8 pounds below recommended, you wont have the sendor trigger.

The best kind is the actual mounted on rim wheel sensor that can detect pressure changes. My guess is this one a) costs more money and b) would "go off" so much more frequently that drivers would ignore it.