A motion detector is a type of electronic security device that senses movement and will then trigger an alarm. These types of detectors can sense motion in total darkness, without an intruder becoming aware that an alarm has been triggered, allowing a higher probability that they will be apprehended by responding agents.

Motion detectors are a key part of many burglar alarm systems. If an intruder happens to gains access to the inside of your house or business, they offer another method of detection. Motion detectors are mainly installed indoors, where birds and other stray animals cannot set them off accidentally. Many indoor motion detectors can be set to a lower sensitivity level, so that if a pet is walking around at night, they will not trigger the alarm.