Motion detection can be acheived in many ways. Motion detectors use infrared arrays and/or microwave sensors to detect motion. Beam detectors sense when someone walking breaks the beam. Floormats sense pressure when someone walks on them. Seismic sensors detect vibration and/or beam stress when someone walks. Caution should be used in the placement of these devices to ensure proper protection and reduce false alarms. A common mistake is having a motion detector that uses microwaves pointing outside a window. Birds and animals, or even people walking by can trigger the device if not set properly.