One of our motion sensors fell off of the wall. we stuck it back on with tape and wanted to test it. shouldn't a red light come on when it detects movement? we tried testing all of the sensors in the house and the main display panel said they were all working fine and detected no movement, even though i was jumping up and down in front of them.
Had one of mine fall off wall also and the light quit working like yours. To test, set the motion detector to delay in the settings and then arm the system. Then move into the room and see if it sets off the alarm. You will have time to stop the alarm from being reported.