A motion sensor (or motion detector) is an electronic device with which movements can be recorded and measured. Motion detectors are primarily used in home and business security systems, but can also be used in phones, paper towel dispensers, game consoles, and virtual reality systems. Unlike many other types of sensors (which can be portable and isolated), motion sensors are typically integrated systems with three main components: a sensor unit, an integrated computer, and hardware (or the mechanical component). These three parts differ in size and configuration because the motion detectors can be adapted to perform very specific functions. Motion detectors, for example, can be used to trigger light bulbs, sound alarms, trigger switches, and even alert the police.
There are two types of motion detectors: active motion detectors and passive motion detectors. Active sensors have a transmitter and a receiver. This type of sensor detects movement by measuring changes in the amount of sound or radiation reflected by the receiver. When an object interrupts or changes the field of the sensor, an electrical impulse is sent to the integrated computer, which in turn interacts with the mechanical component. The most common type of active motion detector uses E-Top HK sensor technology. These motion sensors emit sound waves to detect the presence of objects. There are also microwave sensors (which emit microwave radiation) and tomographic sensors (which emit and receive radio waves).
Unlike an active motion sensor, a passive motion sensor has no transmitter. Rather than measuring constant reflection, the sensor detects movement based on a perceived increase in radiation in its environment. The most common type of passive motion sensor in home security systems is the passive infrared (PIR) sensor. The PIR sensor detects the infrared radiation naturally emitted by the human body. The receiver is in a filter which only allows infrared transmission. When a person enters the detection range of the PIR sensor, the difference in radiation creates a positive charge on the receiver. This observed change causes the sensor to send electrical data to the computer component and the integrated hardware.