[Comparing] Motion sensors (PIR)

There is an important element which in my opinion should be considered when selecting a motion sensor and then included in the benchmark, which is human recognition / whether there are false positives. This is especially important in outdoors where a cat or a bird, even a car can trigger the sensor.

I have tested many different pir sensors so far including Xiaomi/Acqara, sonoff, philips hue and aeotec without the expected results. Just sensitivity levels don’t work.

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The way PIR sensors work makes it extremely difficult (impossible?) to differentiate between humans and animals.

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It is true that “standard” sensors might not work, but I have heard that there are AI based sensors that work, especially in case of those integrated in some cameras.

I have not tried any of those yet and I wonder if any new technology standard might work.

Please note that PIR sensors that are not able to distinguish humans from anything else might be fine in some use cases such as switching lights but not for security as they might trigger false alarms very often.

I have Acqara sensors outdoors which trigger alarms repeatedly sometimes and I don’t even know which kind of events might be happening.

In that case, it’s the AI in the camera that is making the decision. PIR sensors are very simple devices.

You are right, standard PIR sensors are very simple devices and maybe not capable of handling some “intelligence”.

As an example, the aqara is nice, very small, with a very wide angle of detection, but in practice it is very unpractical in some use cases as it triggers many events in situations where nothing is happening and sometimes get stuck in a loop for a few hours.

I wonder if on top of the advertised camera sensors, there are in the market “advanced PIR sensors” as well, capable of really detecting humans.

You missed Roberts point. There are no PIR sensor capable of really detecting humans as that is not how they work. All they do is detect a moving heat source by the pulses it cause on an on/ off infrared sensor through a Fresnel lens.

With these the camera is doing the AI human detection, not a PIR.

Ok, I see now.

Thank you both @Adrian_Rockall and @robertklep for your clarifications.

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In a “pure” sense you are correct.

PIR motion sensors can’t exactly identify what is a human and what is an animal (Eg …say a dog) . etc etc

With the various PIR motion sensors that I’ve experimented with over the years and also researching the way they work I’ve found the good PIR motion sensors will have a chipset in them that filters out (noise) generated by smaller objects such as flying birds, insects, moth’s and small animals…etc etc

My definition of noise being anything that’s “non human”…

For me personally all care about is if 1) someone is in my yard/shed when they shouldn’t be , or 2) My lights reliably turn on when I walk into my garage or my driveway., 3) My lights don’t turn on a million times a night when my pets or flying insects go past the sensor.

These chipsets don’t use modern AI or any fancy machine learning as such, rather just utilise some simple basic algorithm’s. The poorly designed ones just blindly react to the IR sensor with no smart intervention at all.

They aren’t totally prefect at separating humans from animals but from my experience do very acceptable job…

The well designed chipsets also deal with other problems such as a shift in ambient temperature and also deal with situations in which the ambient air temperature is very high and adjusts its overall sensitivity (on the fly) to make sure its works the best it possibly can.

I’ve tried some PIRs sensors which wouldn’t trigger when I walked past them while it was 30c… There are many out there that just blindly react to raw IR sensor input only and don’t have any “intelligent” intervention. These perform poorly when it comes to all these issues. .

On the subject of pets (dogs or cats. etc etc) creating false unwanted triggers some of the good PIR sensors also feature a modified fresnel lens in them that is physically configured in such away that it will ignore moving objects that are lower down. The logic being that humans stand up high and your pets are down lower to the ground. Yes it’s a “stupidly” simple concept but this does help if you have dogs or cats. The marketing term is “pet immune”. Even if you don’t own a pet you will probably get a neighbouring cat stray into your yard anyway, or local wildlife so it’s always a good feature to have.

The PIR sensor that I personally use (the one I mentioned in my previous post) is marketed as being “pet immune”. . Ive found that as long as its mounted higher than 2 meters from the ground my large dogs don’t trigger it most of the time . I never get insect triggers. Never get random triggers 98% of the time .,

Many people have different priorities on what they consider to be the best PIR motion sensor. What is good . What is bad…

On having 6 x motion sensors in my property which I live with and interact with on a daily basis and also trying out a lot of different models if choosing a PIR motion sensor (in my opinion) the three main priorities that you should worry about is (in order) …

  1. Has extremely low false triggers. (Just triggers when a human walks past)… This is the only thing you really want. This should be your highest priority.

  2. For automatic lighting its able to sense you quickly and in a reasonable time… (Not under sensitive). When walking into a dark room you want your PIR sensor to sense you quickly .

  3. The cost… Everyone lives in different properties and have different needs and requirements but it’s not to crazy to at least have 3 motion sensors for a Smart Home. The area where I live , 5-6 motion sensors is not unreasonable to have in a property . Ive seen some over priced “brand name” sensors go for €30 Euro’s. 6 x €30 = €180 Euro’s … That’s crazy money if you ask me . It’s simple tech. They are very cheap to manufacture and produce. If you can sacrifice having remote battery monitoring (which you don’t really need) €5 Euro’s will get you a very good performing 433Mhz based PIR motion sensor like the ones I have.

  4. If having to remotely mount a sensor (no access to power) long battery life is what you really want. Who wants to change batteries on 3 - 6 devices every 6 months. Beside the cost of batteries the inconvenience defeats the convenience. If we are talking motion sensors, which is what this thread is about (not counting “multi sensors”, ) 3 - 4 years between battery changes is quite possibly . (Does depend on the application though ) as long as it’s based on 433Mhz .,

Three other points I can also quickly add .,

  1. Don’t worry too much about adjustable sensitivity levels etc etc. A good PIR sensor doesn’t need tuning or tweaking to stop false triggers. They just work…If range is your worry then just buy a small sensor for short range (in a hallways), or a big sensor for long range …say a driveway.,

  2. Expensive sensors or “Brand name” sensors do not automatically mean good performance. Ive read posts by many people that have purchased expensive sensors that ended up being very disappointed with them. Ive found some particular cheap chinese €5 Euro sensors from AliExpress work extremely well. Money does not mean good…

  3. Spec sheets and tables are ok but they don’t really tell you very much on how good a PIR motion sensor actually is. I would more rely on user reviews on how well a PIR actually performs as most on the market perform like crap. Many are garbage… Even ones with tons of features and cost up to €70 euros. It’s all great to have a list of spec’s for this and that but if they perform like garbage then what’s the point. You just end up with a bunch of small fancy expensive pieces of plastic scattered around your house that don’t actually do what you need them to do… Yaaa , I can read temperature with my PIR sensor but all my outside lights turn on a million times a night and I have to feed them batteries all the time.

You want them to be cheap, you want them to be simple with little maintenance, you just want them to work… that’s it. They are just motion sensors … :wink:

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