PIR SENSOR (PASSIVE INFRARED SENSOR)
A passive infrared sensor (PIR sensor) is an electronic sensor that measures the infrared (IR) light radiating from objects in its field of observation.  They’re  most frequently  utilized in  PIR-based motion detector systems.  PIR sensors are commonly called simply "PIR", or sometimes "PID", for "passive infrared detector". The term passive refers to  the very fact  that PIR devices  don't  radiate energy for detection purposes. They work entirely by detecting  infrared  (radiant heat) emitted by or reflected from the objects.     The PIR sensor itself is housed  during a  sealed metal can  to enhance  noise/temperature/humidity immunity.  There’s  a window  made from  IR-transitive material that protects the  detector . Behind the window there are two balanced sensors.  In its internal structure,  there's  actually a JFET inside (a  sort of  transistor) which  is ex...