I have had the same thing happen to me. I live here in Brownsville, Texas and most of the time the temp stays above 70 F. With a cool front the night temps dip down to the upper 40's and low 50's. The sensor came on this morning while it was 52 F. I drove to work and parked it. It stayed lit all the way to work..about 20 miles. At lunch I went out to the truck and when it started the light never came on. The air temp was over 75 F at that point. When I left to go home around 6:15 the light was back on again...and again it stayed lit all the way home again...the air temp had dropped with the sunset. I looked at all four tires and they looked fine. I checked the pressure right now and I got 30, 31, 32 and 30 neither one a significant difference from each other considering that I am using a fairly accurate dial gauge. Even still it has a +/- 1 psi error.

The point I feel that needs to be made is that it is useless to have a sensor which activates at 28 psi. When they say "significant" air pressure drop they should consider the potential of temperature related pressure drops or rises. The low setting should be around 20 psi. Otherwise the sensor will just be the proverbial boy crying wolf and will get ignored...which is the opposite effect of providing the sensor in the first place.