Making my own bed sensor | Hacker News Reader

Making my own bed sensor

homeautomationguy.io

237 pointsdavikr85 comments

I spent years in a previous job developing acute care pressure pads like these utilizing pressure-sensitive conductive ink. The simple open/closed circuit pads shown here work well above the mattress but (depending on your mattress weight and bed frame structure) can provide false positives when placed below. We had fun stories with our first home testers where many people (me included) planted our elbows and lifted when we turned during the night. This movement was enough of a weight lift over the pad to cause the first iteration of our sensors to trigger. The ability to adjust your bed's unoccupied zero point using an analog measurement, deciding how much weight should be added (or removed) to determine a state change, and over how much time the movement occurred makes a big difference in reliability.

Near the end of my grandmother's life, she was living with my parents and a fall risk. I did this same ESPHome implementation to HomeAssistant to provide us with alerts when she got up on her own in the middle of the night, and it helped my mother sleep much better.

Side note: those other two wires the author says they "have NFI what they do" are most likely wired into the pad as a permanently connected loop. Most monitoring equipment will look for a closed circuit on those wires to detect that a sensor pad is connected correctly and the sensor wire hasn't been broken (ripped, torn, cut, etc).

Damn, why did I never think to use a leak sensor? I’ve been goofing around with building some unusual devices and messing with relays and io pins and arduino and completely missed this obvious solution.

It’s literally a device designed to do exactly what I sometimes need (start an action if a circuit closes) and I just never thought about it even though I know how leak sensors work and that there are ones available. Duh!

Stuff like that is why I love HN. Thanks to the author if you’re reading.

Door/window sensors also work and are even smaller than the leak ones. Just replace the reed switch with whatever.

Some d/w sensors will even have dry contacts specifically meant for wiring in whatever open/close type thing you'd like to use, like a pressure pad.

I didn’t realize there were any that weren’t part of an alarm system/proprietary but it seems the same company makes those too.

I guess that would also be a really easy to do the opposite (if it mattered) since a reed switch triggers the action when it opens, but a leak detector when it closes. Or I guess maybe they do both.

I am curious why the leak detector is bigger if it’s a simpler device. Basically the same thing but without the reed switch right? Maybe just to make room for more battery since you actually care how big the door sensor is.

Door/window sensors usually send a signal on state change from closed to open or the other way around.

I think a leak sensor is more complicated because it needs to detect a somewhat lowered resistance between the contacts, as opposed to the door sensors that will get a fully closed/opened reed switch on activation. Detecting lower resistance with some threshold in a battery powered device that needs to sleep most of the time is probably more complicated. I would guess waking up on a pin state change is built into most microcontrollers, while measuring resistance to make it wake up requires additional components?

Ah! I guess I just assumed water closed a circuit between two probes or something. I’ve never actually used one.

The door sensors on my alarm do make it many different noises on open/close so that one must trigger on both. How cool.

Andreas Spiess' recent video [0] covered some milimetre-wave radar chips whose application includes presence detection at a distance (including if the bed is occupied).

Does anyone know of any bed automatable bed heating/cooling solution (DIY or otherwise) that can work offline of with Home Assistant? I had my eyes on E*ght Sleep but it looks like a lot of the functionality is behind a subscription wall [1] and the device is very chatty [2] and I haven't been able to find any API reverse engineering / firmware mods.

[0]: https://www.youtube.com/watch?v=s-GzUTyIH9c

[1]: https://old.reddit.com/r/EightSleep/comments/1248wgz/buyer_b...

[2]: https://old.reddit.com/r/EightSleep/comments/185cgm4/pod_3_t...

there's bedjet. i find that it doesnt work well with adjustable beds though because when you raise the leg part up, the bedjet hose thing tends to slip off.

https://github.com/pjt0620/Home-Assistant-Bedjet/

I suspect the sleep.me chilipad systems (ooler/dock pro) would work pretty well with adjustable beds since they just run a pair of insulated water hoses to a capillary tube network in a mattress pad. Further, if the hose routing didn't work for you out of the box with those you could DIY something else pretty easily since they use off the shelf connectors (https://www.cpcworldwide.com/General-Purpose/Products/Multil...)

On the bed heating/cooling front, you might try the Ooler series from sleep.me

The older generation Oolers use bluetooth and there are a fair number of integrations including an [MQTT bridge](https://github.com/turmoni/ooler-mqtt-bridge) and a [HomeAssistant integration](https://github.com/PostLogical/ooler).

I'm less familiar with their latest generation which uses WiFi, though there [seems to be an API](https://docs.developer.sleep.me/api/ ) available for it now.

Does anyone know if mmWave could differentiate between my cat and I?

In theory, but probably not in practice. The fancy non-metal-detector airport security scanners use mmWave to detect object through clothing, so the light itself capable of producing high-resolution images. However, cheap home automation sensors are probably not imaging, so you're probably going to be stuck with a single depth measurement.

HomeSeer manufactures a Z-Wave millimeter wave radar sensor that uses imaging techniques to detect motion in specified zones, and they intend to release pet differentiation as a firmware update. I'm seeing enough negative reviews of how it works in practice that I haven't dropped the money on one, but I'm hoping that the technology will improve quickly. It's only $59 too, which isn't much more than PIR Z-Wave sensors. Maybe I will buy one to try out...

Possibly at shorter ranges. Those devices are essentially ‘bag of water’ detectors. You can get some data out of most of them that pertains to distance and approximate size of the ‘bag’.

They generally suffer from exact counts of objects. 2 people close to each other will read like one large person. A large cat close to the sensor could read like a large human at a greater distance.

I looked at mmwave stuff for my own setup but I just couldn't get over it triggering on things like ceiling fans etc moving, curtains rustling.

I think the idea of presence detection is such an interesting problem, really an AI camera is the best solution but nobody wants cameras all over their house. There's also thermal imaging with sensors like MLX90640 which is a very low res thermal sensor.

Seems to work pretty well for the most part, had a bit of a play with it but not actually built something to be put in the home yet but the only drawback is static heat sources like radiators obscuring moving heat sources like a person.

I've done this as well, but I moved to 500kg load cells on the bed legs for reliability.

2 Load cells one on each back leg of the bed. Upside too is I've been able to discern things like, sitting on the edge of the bed to put on shoes etc based on the weights.

Esphome, load cell, and hx711 chip for the load cell comes out to about $40-$50 each leg.

You could get away with using just two cheaper 50kg load cells with some tinkering (i.e. a bracket and screw to send the just right fraction of the load to the cell, on just two legs).

Many years ago, I bought a bed/sleep sensor made by Withings. It worked fantastically, for about a year. Decent sleep measures, circadian aware alarm, all that.

Then it just stopped working. Contacting support thought it might be the pad, and they sent me a replacement. That worked for a while longer, until it didn't. At that point, Withings had been sold to Nokia, and wasn't interested in maintaining their system anymore.

I miss it. I'm sure that this system won't be able to do all the measurements the Withings one did, but thats OK. I've got a watch for that. Def. going to have to try this soon!

Just FYI, Nokia sold Withings back to the founder.

They still sell the bed sensors, don't know if you would have any luck contacting them now. If you do I would be interested in knowing if they respond or not. I recently bought one of their watches and am thinking about buying a scale but I am curious about their long term support.

The new bed sensors post-Nokia are even better. I gave up on the Aura one and just use the new one now.

I did put in a lot of work to make the integration with HA as nice as possible. Their API is nice and they provide it for free. I am secretly hoping they aren't becoming the next MyQ where they want to avoid it.

They even recently launched their Withings+ subscription, so they are trying to bring in more revenue. Their other revenue stream (apart from selling devices) is some kind of reseller program. Let's hope they can make it sustainable so we can enjoy our devices.

This thing is probably well beyond it's warranty, and I got a decent amount of use out of it. But now I've largely moved on, and a simple switch like the op article will probably do everything I need to be fast, and let my Garmin track my sleep

I can attest that the new withings scales are really nice. We've got one in the bathroom and have no complaints

Thanks for letting me know about the scales, I have been eyeing one but didn't want to spend that much on something that I couldn't independently evaluate.

I never thought of using a water leak detector like that nor have ever actually used a water leak detector. I can now create my own pressure plate activated door or true AFK notifier. Thanks for the write up!

I thought the Aqara water sensor technique was brilliant. I wish more device makers would build IoT devices that connect directly to sensors.

Aqara zigbee devices are the first non-lights I've used and they have been great!

The Zooz ZEN16v2 or ZEN17 are also good options for connecting arbitrary sensors via Z-Wave, and the ZEN17 in particular is electrically more flexible (sink or source inputs). That said two water leak sensors will often be cheaper than one ZEN17 with its two inputs. An even cheaper option are door/window contact sensors and desoldering the reed switch to replace it with whatever you want, but it's less convenient for sure. And to wrap it all up, Zigbee devices are often a bit cheaper than Z-Wave.

Fibaro makes a similar device in a smaller form factor as well

https://www.thesmartesthouse.com/collections/fibaro/products...

Water leak detectors are handy. I've got one under every sink and near every toliet now. Should help prevent a small leak from making a huge mess.

I've always thought a Thermal Imaging camera mounted above the bed would be the best sleep tracking system. It could even be hooked up to a feedback loop where if it detects your body temperature rising it can increase your fan speed, things like that. It would be a fun computer vision project.

An averaged heat-map would also help solve the pirennial relationship question of who encroaches on whose side of the bed the most :)

I think you’d find that the actual physical locations of the bed’s occupants are less relevant than you might think to these accusations, ;)

we've done projectd with kinect sensors for fall prevention in hospitals. one con is that many people are uneasy if there's a camera-looking sensor pointing at their bed.

n=? ...would like to know more.

https://www.revk.uk/2023/03/bed-sensor.html?m=1 has another take on the idea after frustration with a "smart" & expensive Withings solution drove him to something different.

Kinky jokes aside, this sort of thing can give a pretty good overview of how much you slept and how well. I use a piezoelectric sensor plate from an "Angel Care" baby monitor. Takes only a handful of passives to safely interface to an Arduino analog pin (safety: The transient from the thing getting jolted not burning out the input pin).

The result, graphed (at 1 minute per sample bin - don't get kinky ideas) gives a very good overview of awake/tossing and turning/really asleep. Which to a lousy sleeper like me can actually be reassuring - yes, I did get some sleep in all this.

Bit off-topic, but having played with HA a bit I always wonder if there is a general strategy on how to deal with failures, i.e. is there a way to make everything go to the default/safe mode in case things stop working? A watchdog-like backup system? And another backup for that :) I get that it's unlikely to happen, but still.. Like:

- some sensor triggers lights on via impuls relay (that's what I have to happen in my home), HA stops functioning, lights remain on. How to make sure instead they're turned off? I get that not using impuls relays but relays which need to be driven high constantly might be one step in the right direction, but that would still assume whatever line the relay is driven with is pulled low when HA stops functioning.

- you setup HA to instruct your home battery to charge during off-peak hours, HA stops functioning during off-peak, battery is left in 'charge as much as you want' state. Unless battery has functionality to tell it 'charge max x hours' it will try to keep charging, whereas it would be nicer if it wouldn't

- same for heating: leave for vacation, tell HA to put heating in low power mode but to start heating the house again in normal mode 3 days before I'm back (because that's roughly the amount of time needed with low temp heating to get everything warm again). HA stops, I come home to a cold house.

At least for the lighting related concern, I personally use both Zigbee bulbs and switches. These can be bound together so the switch will directly tell the bulb to turn off/on without intervention of anything else. This results in a faster response and working light switches even when home assistant is down.

Ok but can you tell them 'go to state x when HA is down'?

Sensor shows 2 people in bed, when you're not home.

"That can't be right; it looks like there's a sinusoidal error signal in the sensor readings..."

"Wait... something is modulating that sine! The frequency is rising."

"I really need to tune the debouncing algorithm, these errors are driving me nuts"

yeah this is creepy, i hope the writer's love life is okay.

It's not creepy.

Typically one of the first types of automations you do is presence and motion detection, for simple things like turning off lights when no one is home, turning on lights when you enter a room.

Then you find edge cases like wanting the lights to turn off when you're in bed, but not turn on if only one person gets up in the middle of the night.

If you want to automate any of these things then it's necessary for the system to see the events.

In my experience, people say it's all worthless, until they experience it themselves.

i'm probably reading too much r/amiwrong and r/aitah

I can totally see the utility of having lights that turn on/off because I've gotten into bed for the night. I want no part of it, but I get the frustration of finally getting warm and cozy, just to realize that I left the kitchen light on or something and I can see it reflected down the hall, or through the window on the fence.

I have smart outlets for my christmas lights so they turn on at sunset, and that's about as far I want go.

Bed sensor is unnecessary to turn off kitchen lights from bed. You need smart bulbs everywhere to be able to turn them off, and once you have that you can turn them off with an app on your phone, a smart speaker, or if those get annoying you can just buy a smart button and leave it by your beside like I did. No wiring needed

>Bed sensor is unnecessary to turn off kitchen lights from bed.

"Unnecessary" is entirely a judgement call. Anything more than alligator clips (to make the connection latching) on bare wires to dis/connect the power to the light is arguably "unnecessary".

The whole point of the automation is so you don't have to remember to do it. I'd still have to remember to open the app, or slap the smart button, or whatever. Rolling over to slap the smart button doesn't disrupt my descent to sleep as much as walking out to the kitchen to turn off the light, but it is more disruptive than just falling asleep. This is to say nothing of using a smart speaker, and dealing with the 1-2 punch of waking up enough to say "turn off kitchen lights", and dealing with the consequences that spring from my kids' special sensitivity to my and my wife's voices near bed time.

Again, this isn't for me, but I fully understand the need.

That's fair but what if your wife and/or kids are grabbing a drink from the kitchen and the turned off the lights be getting into bed?

Yeah, super weird thing to be wrapping automation and detection around, I'm really unsure of the use case other than this.

This would also be a great prompt for a short horror story where someone discovers more people have been living in their house than they believed.

The moisture sensor component. I can’t stop laughing picturing a readout like:

“Greg’s Bed …. Wet”

I often find reading these sort of descriptions amusing, for the strange mix of "hey, cool seeing someones DIY project" vs "I just don't understand why". I guess my personal value on hacking up your own stuff is just way higher than that on home automation...

To each his own is a good rule when it comes to hacking/geek projects.

I've so often been asked "but why are you doing this" or suggested that I go and buy the stuff that I'm making.

I find it very annoying. I find most people who ask so such questions won't "get it" even if I explain.

But I do understand that most often people are trying to be helpful. They can't imagine going through the ordeal that I'm going through for something of no value to them.

Oh I would never ask someone why; let a thousand flowers bloom.

I just find I get tickled by the ratio of my interest in how someone solved their problem to (my) lack of interest in the product in this particular genre at least.

"To each their own" is a good principle :)

I guess a different way of looking at it is this, I'm laughing at myself realizing that I would happily spend hours helping you figure out a hardware/software problem in your home automation setup, but I wouldn't spend minutes automating my own home. probably. maybe the right itch hasn't presented itself.

For me, most of the amusement was that my mind went in a very different direction upon seeing both "leak sensor" and "bed sensor" being mentioned.

Count me in the "I just don't understand why" group too --- I work with enough software in my day job that I really don't want more of it in my life beyond that.

I specifically do my own projects because day job software isn't really that fun. It's someone else's requirements, you are blocked by others, etc.

The more I do of my own projects the higher is the fun to frustration ratio of doing software/projects.

The trick with the water sensor is really neat, might have to look more into that. I also wish that more companies would design some of these building block smart devices for us hobbyist. Don't tie it specifically to water, maybe have a pot to trim the sensitivity, et voila you now have a pretty handy all-round ADC thing.

For my bed detection though I just have Tasker on our phones telling the system when they charge. If it's after a certain point of day and our phones are charging that's a good indicator that we've gone to bed. Doesn't require any extra hardware, making it super cheap. Although accuracy obviously won't be 100%.

Force sensor resistors can be had for $3-$8 a piece, would they not also do the trick? ESP32 is such a great platform, can you not just make an HTTP request depending on force to a Home Assistant API endpoint and skip the leak detector as a conduit?

yup FSR, thats how I do it

Yes but Zigbee is great.

What the leak detector gives you is a long battery life.

You can achieve it with DIY but if you want microamp-level current consumption you’ve got to do without a lot of the components that appear on dev boards

Great project! Until now I do not have anything connected to my bed, I can't sleep with something attached to my wrist, so no sleep data. Tracking the sleep would be really great, but the current solutions seem not right to me.

I would welcome a system, which may be used as a pod sensor, like the mentioned EightSleep or Withings, both not visible. But I want to set when something is radioing around my bed. Just like on my smartphone, where the flight mode is activated, I would like to set the device so that the data is only synchronized via WLAN or Bluetooth when I am no longer lying in bed.

> I can't sleep with something attached to my wrist, so no sleep data.

Another option would be Whoop that you can add to your underwear.

Expensive I know, but it works very well.

I use a Google Nest Hub for two weeks now. It has sleep tracking via IR cameras. It promises this is all on-device. I think it is reasonably accurate. Google said it is going to charge 8 euros per month for it starting January 1st. I’ll stop using it then

I see the photo of the sensor atop some springy bed slats, but don't see mention of how the sensor setup distinguishes the weight of of mattress above springy bed slats from when a person is atop.

I have a similar setup with the same kind of sensor. It just doesnt register the matress at all. My guess is that the matress weight is evenly distributed so it doesnt actually put that much pressure on the sensor.

matress are around 40, maybe 50kg/m3.

water is 1kg/dm3, and acording to this website (https://www.aqua-calc.com/page/density-table/substance/human...) human is arround 1000kg/m3 which make sense.

So, yes matress is light compared to human, I guess it does nothing to the sensor pad.

I love reading about implementations like these. I love the technology behind it. But I’ve never read about a project like this and wanted to automate my house in any way. Maybe I’m a weirdo, but I enjoy getting up and turning on the light, and making coffee. I’d be somewhat bored if it was all done for me. I would miss the routine.

I need one of these to stop my cat from turning on the bedroom lights when he’s hungry. Unfortunately with HomeKit doing automation like this the easy way involves converting the action into a shortcut, which comes with execution delay.

How does the water leak detector work? What's supposed to go onto those contacts?

Water

Water.

It works by having water (or another conductive liquid) provide a path between the contacts.

Interesting, the terminals really look like those screw terminals you attach cables too.

I'm guessing they sell some kind of extension to attach to those terminals. For example, here's what the $12 water alarm in my basement looks like: https://www.amazon.com/Glentronics-Inc-BWD-HWA-00895001498-B...

I used to use the withings bed sensor combined with IFTTT to boil my kettle downstairs when I woke up in the morning.

I wonder if it could distinguish between a human and our 35kg dog who often lays on the bed during the day.

The dog also deserves to not be suddenly flashed with light when it is lying in bed!

Yeah, but he tends to lie across the middle of the bed so would be detected as two people and send the house into bedtime mode. :-)

Mostly I'm just jealous that the dog spends more time in my bed than I do.

I thought the sensor can be used to check if my kids are making their own beds properly.

Obligatory:

https://biggaybunny.tumblr.com/post/166787080920/tech-enthus...

I think it makes a big difference if your home is running on open source stuff or not.

I wouldn't be comfortable with Google or Amazon running my house but if it's stuff I flashed myself from github it's a lot better.

Absolutely. These things basically say to others what is going on in your own home.

To have domotic connected to a wifi or internet is a no go.

If I were to have it for a really heavy weighted reason, seeing the current state of things, I would have previously to spend months developing non standard custom encryptions with hidden rotatory keys methods of my own, custom non standard protocol, connections monitoring and so on. And even like that I would feel cautious, It would need to be a real weighted reason.

I can not understand how is it possible the people is using IoT without needing it, totally naked, without even demand any kind of protection designs, or/and even giving third parties all that information, because it can be even dangerous.

Semi-Of-topic:

I would like to have a lidar vacuum cleaner, for to clean effectively zones without collisions with a mapping, etc. Past year I took a look to manufacturers and models, but it seems that from the beginning, when they started to sell them years ago, those devices with mapping require to be connected to the wifi and to the internet; they submit the mapping of your home to internet, the manufacturer server, for to let you make use of such mapping for to run the vacuum cleaner. Oh my...

I could not even find more information on the forums (in several languages), people don't seem to find this as a inconvenient? for me it's an absolute no go.

All of this is approaching the classic dystopian books that should remain in the sci-fi section.

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