Thanks for the info everyone. Jsnlong... I do use cheap batteries, but I've been using them pretty much all along. Yes, the temps I gave are daytime highs. It is getting much colder at night. The trend overall is warmer temps though. The problem seems to have surfaced during the warmer temps. We just got a little bit of a cold front and the problem has nearly disappeared for the time being. I don't think the issue is operating temps, because it has worked fine on this door for over a year in near freezing to well over 90. I also mentioned the one other problem sensor that is indoors in the heated space. It showed the problem of the contacts not seeming to be connected to the sensor last night in that it did not respond to the window being opened or closed, but tonight it began working again with no problem when I opened the window. This is a little confusing, because I was under the impression that these normally closed sensors would transmit an open status if there was a problem with the wiring from the contacts to the sensor, but in this case, it just transmits a closed status even though it does not register contacts opening and closing. It will even return to a closed status if you press the test button. That means you could have a contact failure and not know it had occured, unless you happened to open that particular window. It seems that the sensor does not monitor whether the contacts are closed on a constant basis, but only registers a change in state. I guess the other possibility is the problem is not in the sensor body itself as in a solder connection on the circuit board, but might be in the contact end. Is there some malfuntion of the contact itself that could make it tell the sensor it is closed when in fact it isn't?