Occupancy Sensor Vs Motion Sensor

Can anyone recommend a true occupancy sensor… A sensor that “Continuously” reports on room occupancy rather than reporting motion… and then timing out.

Also… is there a way to “Reset” a motion sensor so that it could “Act” as a occupancy sensor.
I’ve got several Z-Wave PIR motion sensors but as of yet been able to reset them so that they could be used as occupancy sensors


Post Note:
I did just find this on another site…

The Ecolink sensors have header pins that can be used to set the sensor to “Test” mode. In test mode the sensor will wait only 5 seconds before rearming. From the manual -

“Test jumper installed: Will wait only 5 seconds after motion detected to check occupancy and communicate status.”

It is hard to report true occupancy. But I think a good CO2 sensor does the job maybe it’s best. It detects humans (and pets) very well. Maybe you should look into that.

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Huh… That’s one I definitely didn’t think of… I imagine it would not have the responsiveness of a PIR …

Not sure how reliable CO2 based presence detection is, but you could always combine it with a PIR. The PIR would give you responsive fast presence information and the CO2 would be longer term, like if someone sits still reading or watching TV. Combining multiple sensors is always a good way to increase reliability. A basic way would be a simple logical OR. A better way in your case would be a temporal order based logic: presence is detected when either PIR is currently triggered OR [ CO2 is above threshold AND PIR triggered at least once earlier ].

I can imagine you would need to recalibrate the CO2 threshold from time to time and also manage longer term trends (higher CO2 concentrations in winter when not much outside air will come in). So you probably can’t use a fixed detection threshold on those. Would be interesting seeing some graphs about how well that works. @frits1980, do you have some data to share ? Maybe a longer term CO2 level graph showing when people enter / leave a room ?

And what happens if the person in the room opens the windows ? :slightly_smiling_face:

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Actually I don’t use them. Because I was on the market for air quality sensors I stumbled upon this post: Air Quality sensor hardware advice - #9 by richieframe
Which explained it very well I suppose. So maybe direct more questions about this to him?

The best way to detect occupancy is to have a sensor grid of many kinds, all working together.

PIR, Radar, Thermal, CO2, Laptop use + RSSI, Vibration, Acoustic, Door/Window sensors, Computer vision, Bluetooth tracking, etc

Combine that with a variety of “obvious” override states, such as:
Alarm system armed away = nobody is home
Mobile device locations = if one is “away”… they to do not need to be accounted for
Certain button presses = my bed has 2 identical light control buttons on each side for me and my wife, if the door is closed, and I press a button (on my remote), and the door does NOT open, then I am for sure in that room until at least the next time the door is opened

You can also aggregate rooms depending on house geometry, for example combine livingroom and kitchen so as people move between them there is no complex logic involved, or you can treat certain rooms as “ephemeral” like the bathroom, so it only reports as “occupied” but your person state is still in the previous location.

My laptop RSSI will tell for sure if it is either in the living room or my office which are the only 2 locations it would be

For CO2, you are looking at trends and levels, if someone has been in a room and the level stabilizes, it will invariably go down when they leave, and if it is trending up (but other rooms are not) then the room is most likely occupied… unless there is a change in ventilation which will cause it to tank. How breezy it is outside can have a massive contribution to CO2 levels if a window is even slightly opened.

If you have your HVAC fan on all the time it will also cycle air out of an occupied room, but not too much that it renders air monitoring useless. An occupied common area like a living room can stabilize at about 1000ppm even with continuous ventilation, depending on how “leaky” your house is.

A quality device will adjust for temperature and humidity automatically, and usually autocalbrate unless the conditions are not suitable, like a poorly ventilated space that is never unoccupied

Here is my livingroom CO2 sensor levels for today once people were up, which happened to be a rather blustery day. At 2:27p a door was opened for ventilation, at 2:50 it was closed since we were in the process of getting ready to leave, at 3p we drove away, 1 person got back at 4:20p, another at 4:50p. You can see almost every single event on the graph, but it is hard to interpret without additional data and context.

This is a week’s worth, you can see it tank at times, due to ventilation, and you can see some nights it hovers around 500ppm, a window is most likely open, you can see exactly when I closed it at around 3am on the 21st as it starts to trend up to baseline.


Wouldn’t one get pretty far with only a camera per room doing human detection? I’m just a curious wanderer on this topic, but that is genuinely what I’m thinking.

@richieframe, interesting stats, thanks for posting those. The data does look noisy and there’s a lot of collateral correlation involved (windows, vents, HVAC), but depending on your situation it definitely looks like you can get some good data out of that with the right filters and compensation. Interesting approach for sure. Might get myself a CO2 sensor to start messing around with over the holidays :slightly_smiling_face:

Probably. But a lot of people (myself included) find indoor cameras creepy.