We got a "Replace battery" sensor for a room. Replaced the battery. Still have the "Replace battery" message. Swapped out the new battery with one in another room that's working fine. Still get the "Replace Battery" message in the original room (now with a known working battery.) This is the SECOND glass break sensor this has happened to. After 30 minutes on the phone last time with a rep, they finally sent us a new glass sensor, and the same battery worked fine in it. Getting REALLY tired of this.
And the answer is (from the technician who came by): you have to hit the little metal strip inside the sensor several times when you replace the battery. Something the on-the-phone troubleshooters don't apparently know.