Motion detectors are devices that detect moving objects. They are typically integrated within systems that automatically perform tasks or alert users of a specific or any motion within an area. They form a vital component of automated security, lighting control, energy efficiency, and home control systems, among many others. These sensors, particularly electronic ones, usually contain either an optical, a microwave, or an acoustic sensor, besides a transmitter for illumination. Passive sensors, on the other hand, will only sense signals emitted by a moving object. The changes in the microwave, optical, or acoustic field within a particular proximity of the device are interpreted via its electronics based on motion detection technologies like PIR or passive infrared, ultrasonic, microwave, video camera, or tomographic motion detection.
The most inexpensive types of motion detectors can sense movements up to distances of at least 5 meters or approximately 15 feet. More specialized systems are typically costlier, but they do have longer ranges. Tomographic motion systems, for instance, can cover larger areas because radio waves they detect are at frequencies that penetrate obstructions and walls. Motion is also detected in multiple locations and not just at the transmitter’s location.
Motion sensors find great use in a wide range of commercial and domestic applications. A common application is for the activation of automatic doors in public buildings and business establishments. Motion sensors are also commonly used in place of occupancy sensors when activating indoor lights in walkways, staircases, and lobbies or when turning street lights on. In smart lighting systems like these, energy is conserved by powering lights only for the duration of a timer after the occupant has left the area (presumably). Electronic motion sensors are also widely used in burglar alarm systems that alert home owners or security services of a possible intrusion.