A passive infrared sensor (PIR sensor) is an electronic sensor that measures infrared light radiating from objects in its field of view. All objects omit heat in the form of infrared radiation, usually this light is invisible to the human eye, but it can be detected by electronic devices designed for such purposes.  A PIR motion detector do not detect motion, rather, they detect abrupt changes in temperature at a given point.  They are commonly used in security lights & burglar alarm systems, when a person in the field of vision of the PIR moves it activates the security light or burglar alarm.

 

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