Hi guys I used to install CCTV and Intruder systems and you may not be aware but the alarm detectors that have passive infra red and microwaves known as a dual tec can cause the exact problem that you are experiencing. We had a site that proved it to us using a spectrum analiser.
From observation if the detectors have more than one led i.e. green red and amber it most likely has a microware. You can cover the detector with silver foil to prove this but I wouldnt recommend it as it may have anti masking make sure you don't leave the foil over the detectors at night.
