Homey Community Forum

[HOW TO]: Create a Zigbee chair sensor for better activity detection

I wanted to automate the lights in my studio: Lights on when I’m working, Lights off when I’m gone. But I’ve discovered that I have a special set of ninja skills: I’m able to sit long enough behind the computer without significant movement to disable the motion detection. Really annoying to have to wave to the sensor for some attention every couple of minutes. (and I don’t want to ramp up the idle period to 15 minutes).

Then I thought it would be really convenient if those car chair sensors to detect people (to put on the seatbelt) where inside the desk chair. Little search on Uncle Ali, and found some universal chair sensors. Great! https://nl.aliexpress.com/af/universal-car-seat-sensor.html

I’ve modded a Aqara window Zigbee sensor to connect it to the seat sensor. It really works great!
I figured I’m probably not the only person with these ninja skills, so here’s a tutorial how to detect seat presence.

These are the parts you need

Use a small flat screwdriver to wedge open the enclosure

Don’t loose the small reset “button” (don’t forget to reinstall if it drops out)

This is the PCB.

Desolder the reed contact (the glass thube). It helps if you add solder first.

Solder the seat sensor wires like this

Cut a hole in the enclosure (make sure you cut the correct side)

Press everything back together and you are good to go!

Pair it with Homey. Invert the contact alarm in the settings and put it on the chair.

The best place is directly under the fabric. But I’ve put it under the seat-cushion. I’m using a game chair and there’s a flat metal plate below it.

If I sit, the seat gets pressed enough to push the sensor for detection. It didn’t detect flawlessly this way, so I added some strips of that sponge isolation tape (that stuff you put on windows to eliminate draft) on the top of the sensor. Now it never failed to detect seat presence under the seat.


Nifty, compliments!
Could come in handy for other purposes too where you want to detect something, based on pressure.

Can you show a picture of the sponge isolation tape as well? Not sure, what you meant by that and how it increases reliability.

I was afraid someone would ask that :sweat_smile:

It’s already taped under the cushion (sensor has double sided tape). But I’ve managed to take a picture.

Because I put the sensor under the seat cushion (instead of directly under the fabric) the pressure gets way more distributed so the pressure point’s sometimes don’t get enough pressure for detection.

By putting a strip of sponge isolation on top, the sensor gets more pressure. It depends on the situation and probably needs a bit of experimentation if you want it below the cushion like I did. Try it first without it. You also don’t want too much pressure otherwise it might detect while nobody is sitting on the chair.

Ah, clear. Thx!

Instead of the doorsensor you van use a aqara watersensor. It has two screws in it where you can put the wires under.


That seems indeed an easier solution. But I don’t know if this detects as simple “activity” inside Homey. If the water sensor gets triggered over here, all kinds of alarms activates (including Apple HomeKit) which is a less desired effect for this usage. The two screws are also highly sensitive. A high resistance between the two screws also triggers it. This might trigger falsely since the pressure switch plates are really close to each other.

But I haven’t experimented with it. It might work fine. So if someone does, please let us know :grin:

I might try this out under my matras… To detect if anybody is present in bed. I guess the sensor will not heat up if it is between the matrass and the layer above?