Can you provide some common scenarios that cause motion detector false alarms? We don’t have any pets and everything in the room seemed undisturbed, no books falling off a shelf or pictures falling of the wall so we are left puzzled as to why it alarmed.
Passive infrared motion detectors are activated by changes in heat signature in their field of view. Common causes for false alarms on PIR motion detectors could be anything from heating vents, direct sunlight on the lens, pets (which sounds like is not an issue in this case) and even insects crawling across the lens.
Is this motion detector directly facing any windows and how far away are they?
Does it get direct sunlight? Could there be any vents nearby?
Here is some additional information that may help you. While it is specific towards 2GIG panels and not Qolsys, however, all PIR sensors have similar false alarm concerns.