Motion detectors are electronic devices that detect physical movement in a specific area. They use various technologies, such as infrared or microwave, to detect motion and then trigger a response, such as an alarm or a notification. Motion detectors are commonly used in security systems to detect intruders or unauthorized access, but they can also be used in other applications, such as turning on lights when someone enters a room. They come in various types, including ceiling-mounted, wall-mounted, and standalone units, and can be used both indoors and outdoors.