When you sits down, the lights turn red
My friend Jacob built himself an office chair out of an old Tesla seat. The seat still had its occupancy sensor in it, the same little pad that, in the car, knows when to start nagging you about a seatbelt. We hooked that sensor to an ESP32 and hooked the ESP32 to his smart lights. Sitting down now turns the room red.
Jacob, sitting down, on demand.
The piece that already existed
Modern car seats ship with a presence detector in the cushion (usually a pressure mat or capacitive pad) wired to the body control module so the car can decide whether to fire the airbag, sound the seatbelt chime, or skip the passenger entirely. Once a seat is out of a car, that sensor is just a switch-ish thing with two wires hanging off it. Exactly the kind of part that wants a second life as an input pin somewhere.
The bit we added
- ESP32. Reading the sensor on a GPIO with a hardware debounce so a wobble in the chair doesn't cause a strobe.
- Light control. A small HTTP call out to the smart-light API on sit-down and another on stand-up, switching between "Jacob is at the desk" and "Jacob is not at the desk" scenes.
- Wi-Fi reconnect. The usual ESP32 boilerplate. The rig lives behind the chair, nobody is going to push a reset button.
Why it's worth talking about
It is a five-minute project that hits every part of the home-automation stack: a real-world sensor, a microcontroller, a network, an API, a physical effect. And the payoff is good. There's something specifically funny about a chair announcing its occupant by changing the colour of the room. Small projects can be high-density.