That sounds like a neat hack, but you have to be careful with the microwave’s internal circuitry—those components aren’t meant for low‑power DIY use. I’d start by isolating the IR LED and photodiode, then run a simple voltage divider to read the signal with a microcontroller. If you want something that won’t fry, a cheap PIR sensor is a lot more reliable, but if you’re up for the challenge, we can tweak the circuit and keep it low‑maintenance. Just keep the power low and the wiring tidy, and you’ll have a motion detector that won’t drain the grid.

Sure thing. Grab a 10 kΩ resistor and a 4.7 kΩ resistor. Connect the 10 kΩ from the IR LED’s anode to the microcontroller’s input pin. Tie the junction of the two resistors to ground. That gives you a voltage between 0 and about 3.3 V that the MCU can read. Make sure the LED is powered from the microwave’s 12 V supply, but use a dropper to bring it down to 5 V or less with a small series resistor, or use a zener if you’re worried about spikes. Then in code just read the analog pin, map the voltage range, and trigger on a change. And yes, if it starts a fire, blame the coffee maker—just say it’s a safety test.