Ok... I haven't an idea where to look with this one...
I have not been out to the site yet, but the customer claims the alarm goes off when they turn on the ceiling fan.
Ok... I do have an idea. This was a takeover, and I didn't run any of the wire. I wonder if one of the wires is parallel to the fan wire in the attic, and its getting an induced voltage spike when the motor starts up... I don't know.
I've always been careful of that sort of thing myself and I have never experienced that on an alarm.
I guess I also need to go listen to the fan starting up. LOL.