A Passive Infrared Detection (PIR) motion sensor is used to detect object movement. We can use this sensor to detect human presence. You can find PIR sensors at SeeedStudio (https://www.seeedstudio.com/PIR-Motion-Sensor-Large-Lens-version-p-1976.html), Adafruit (https://www.adafruit.com/product/189), and SparkFun (https://www.sparkfun.com/products/13285). A PIR motion sensor usually has three pins: VCC, GND, and OUT. The OUT pin is the digital output; if we get value 1, it means motion is detected.

You can see the PIR sensor from SeeedStudio here:

There's another PIR motion sensor from SparkFun, the SparkFun OpenPIR: https://www.sparkfun.com/products/13968. This sensor provides analog output so that we can adjust the motion-detection value. Here's how it looks:

We learned how to use this sensor in Chapter 2, A Smart Parking System. You can try using it to detect human presence.