Arduino HC-SR501 PIR Sensor

• You can detect motion with PIR sensors, often known as "Passive Infrared" or "IR motion" sensors.
• Infrared radiation (IR) is emitted by everything, and the more heated an object is, the more IR it emits.
• PIR sensors can sense motion because they can detect changes in the average infrared levels inside their detection zone, such as a minor increase in temperature when a person enters a room.
• This one is fantastic because it can be read directly from the Raspberry Pi's GPIO input and powered by the device's 5V output (the sensor has a digital 3.3V output!).