My neighbour's burglar alarm has suddenly taken to going off at random. She has 3 IR sensors, one of which goes on and off when you wave your hand at it, but the other 2 now seem to be permanently illuminated. Does this suggest faulty sensors? I imagine it would be a coincidence for both to fail at the same time, especially as they appear to be on separate cables. Could a fault elsewhere cause 2 out of 3 not to work?
Any advice welcome