Have you been spending too much time sitting on your backside setting up new integrations for Home Assistant and writing firmware for ESP8266 nodes? Perhaps it’s time that you built yourself a chair occupancy sensor to quantify the exact time you are at your desk.
Or maybe you just want the lights to stay on whenever someone is sitting at a desk. Want to save some energy? Have your PC put into sleep-mode whenever the chair has been empty for more than 30 minutes? A chair occupancy sensor might sound like a gimmick at first but there are some actually useful use-cases once you start to think about it.
That is exactly what Home Assistant community member parrel decided to do. And in true Home Assistant fashion, it is a DIY sensor hacked together from an Aqara window/door sensor and a car seat pressure sensor.
Because this project uses a Zigbee sensor it is free of any wires and can be powered for many months using only a single coin-cell battery. And because you can order all of the components directly from China, the whole project will cost you only about $10.
Hardware you need to build the chair occupancy sensor
How the chair occupancy sensor works
The electronic part of Aqara window/door sensor used in this project uses a so-called reed switch. The second and smaller part of the sensor is simply a magnet. When the magnet is close to the reed switch, the contacts in the reed switch are closed, the circuit is completed, and the sensor tells you that the window or door it is attached to is closed. When you open the window or door, the magnet can’t close the contacts and the circuit is broken. It is such a simple bit of electronics that even I understand it.
In the chair occupancy sensor, the magnet is no longer used and can be kept for other projects or used on your fridge. The reed switch is bypassed by attaching the wires coming from the car seat pressure sensor to either end. If you wanted, you could also completely remove the reed switch.
Instead of having a magnet close the circuit this chair occupancy sensor now uses the car seat pressure sensor to close it. All that is left to do is to insert the sensor into your chair and the project is complete.
As you might have guessed, you are required to solder the wires from the car seat pressure sensor to the Aqara window/door sensor. Apart from that, this project is very straight forward and uncomplicated.