Motion detection can be achieved by either mechanical or electronic methods. When motion detection is accomplished by natural organisms, it is called motion perception. The principal methods by which motion can be electronically identified are optical detection and acoustic detection. Infrared light or laser technology may be used for optical detection. Motion detection devices, such as PIR motion detectors, have a sensor that detects a disturbance in the infrared spectrum. Once detected, a signal can activate an alarm or a camera that can capture an image or video of the motioner.