PIR sensor is widely used as motion sensor to detect the human or animal activity in a particular area. All objects emits heat energy in the form of radiation which can be visible when the wave length reaches in the visible spectrum. But there are certain ranges of radiations which could not be recognised with human eye but can be sensed with certain sensors.

Infrared radiation emitting from human or animal body can’t be sensed by our naked eye but can be detected by pyroelectric sensors. The sensor which detects infrared radiation emitting from other objects are called passive infrared sensors. They are called “passive” since the sensor itself doesn’t emit any IR radiation but passively sense the radiation emitting from the source. . It is now an unavoidable entity in building automation systems

Working of PIR Sensor

The sensor consists of two Pyroelectric IR sensors which are placed adjacent to each other. In normal case the infrared radiation reaching on the sensor will be same for each of the sensors but it changes when a second object like human or animal having higher body temperature approach in the sensor range. This change can be taken as a sign of motion in the particular area.

PIR sensor has wide range of applications in

Automatic door open: The doors can be controlled by sensing human presence in the vicinity, highly useful for physically handicapped personals.

Escalators: Often we have seen escalators functioning in malls and airports without any users, using these technology escalators will function only when users come near its vicinity.

Burglar alarm: The PIR based motion detector is very commonly used in burglar alarms as the sensor picks up any unusual movement in the area.

Automatic light systems: How often we have wished that the light in our room gets turned on the moment we step our foot inside, well the PIR sensor exactly does that.

Military Surveillance: Since PIR covers a vast area, it is perfectly suitable for surveillance across borders.