PIR "Passive Infrared"sensors allow you to sense motion, almost always used to detect whether a human has moved in or out of the sensors range.
How to Use PIR Sensor
The PIR sensor have 3 pins:
Power: 3-5 VDC
Output: High (when motion detected)
Low (no motion detected)
Ground: connected to ground
The output pin will go "high" to 3.3V and light up the LED when motion detected.
Input Voltage: DC 3-5V
Output signal: 3.3V (motion detected-output high)
Detection Angle: 110 degree
Detection Angle: max 7 m
How Does The PIR Sensor Work
The PIR sensor itself has two slots each one of them is made of a special material that is sensitive to infrared. When a warm body like a human or animal passes by, it first intercepts one half of the PIR sensor. This causes a positive differential change between the two halfes. These change pulses are what is detected.