Pets, rats, and insects may set off some motion detectors.  Pet owners should make sure their home security system has “pet-friendly” sensors, to avoid any false alarms due to the pets roaming around the house. Unlocked or buckling doors and windows are other typical sources of false alarms. A two-piece sensor is typically used for window and door security, one mounted on the frame and the other on the window or the door. The alarm will ring if the connection between the two contacts is broken. A partially closed door or window can be blown wide open by the wind.