When the Pi is shut down in software, the Arduino can sense that the Pi isn’t on any more and disconnect the power. The remote control is used to turn the Pi on.

The IR Detector proximity sensor is designed to be compatible with both Arduino and Raspberry Pi platforms, making it a versatile choice for hobbyists and professionals alike.

The part list consists of one Arduino, two resistors, and one IR emitter. That’s right, an emitter. When an LED (IR or otherwise) is reverse biased it can act as a light sensor.