https://community.home-assistant.io/t/fsr-the-best-bed-occupancy-sensor/365795
This is the best write-up I've seen - essentially a force sensitive resistor on the bed slats and an ESP32 will get you the results you're after.
this post was submitted on 17 Mar 2025
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I’ve got parts on order for this very project, should arrive this week.
I previously tried using one of those large pressure mats but it didn’t work under the mattress.
Aliexpress has load cells that go up to the hundreds of KGS. One of those, an esp32/pico and some wiring and you should be good to go?
Couldn't find the exact one I ordered a few months ago, but this type of pressure sensor aliexpress link is apparently a common bed occupancy sensor type used when building medical beds for hospitals and care homes so staff can be alerted when a patient gets out of bed. I'm not sure the specific model I linked is quite right specs-wise, but the idea is that it goes on a slat or other surface between the matress and the frame that doesn't necessarily get the full weight of the occupant, but still gets enough to measure on the sensor.
This. I bought a few myself, but didn't have time to put them together with ESP32/program them with ESPHome
I’ve got this setup: Two of those flat contact sensors that are designed to go under a mat, connected to an ESP32 running ESP Home. Some people use leak sensors with screw terminals instead of the ESP32 and attach the contact sensor that way. My use case is that we’ve got cats and motion sensors, so when everyone is in bed, the lights don’t react to the motion. Also, alarm system goes into night mode, any reminders before going to bed also fire. There are a set of rules about whether the doorbell can be heard in the bedroom, and also the light comes on in the night if someone gets up.
I've worked on such IOT devices for the hospital.
How about mm radar?
I grabbed a couple of Ali last month to use for lighting sensors for the hall and toilet, not set up yet
Those don't work well if you stop moving for extended periods of time, and do not see through bed sheets in my experience
I have an Aqara FP-2 doing just this thing. It works pretty well after setting up zones. Those get pulled into Home Assistant and then you can tie those to automations to control lamps or what have you.
I also used a mmWave sensor in the past for this, one from a youtuber. Worked well enough for my case, but it had some interruptions during the night.
I don’t have one myself, but several of the guys on YouTube use them. See “The Home Automation Guy” or “Smart Home Solver“. I can’t remember the brand they use.
Use car occupancy sensors and an esp board. That's what I did. I stuck them to corregated cardboard and put one under each side. Aim for the butt area as that seems to apply the most pressure. I would order 4. 2 for each side because you can put them in parallel to divide the resistance and make them easier to trigger.
Buy them on AliExpress or eBay.
I've never done anything like this, but would it be possible to place such a sensor between the mattress and the frame instead? That would result in a fraction of the load due to the distribution of the weight. The challenge would be to set the threshold right.
I believe that's how most people do it. It works for me. You can also put two in parallel or just add a resistor across the leads to divide the resistance to make it more sensitive. If you used a potentiometer it would make it easier to adjust to hit the exact threshold.
@bus_factor Some of the #mmWave (Radar) Presence sensors may be able to detect bed presence through the mattress, mounted under frame. I have not tried this yet but I’ve been planning to. The Aqara FP-1 or Aqara FP-2 are candidates, but maybe too pricey for an experiment. The Apollo MTR-1 is far less expensive and excellent for short range. It is also small and with a sturdy enclosure you could easily place it between and mattress. These sensors can pick up very small motions, even the human heartbeat (sometimes through walls). I use both Aqara (easier set up) and Apollo MTR-1 for room and zone presence detection, with #HomeAssistant for integrated automation.