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Awesome, I wonder what this combined with some electronic automation can do. Eg, I walk into a room and lights turn on, i walk out, lights turn off (depending on time of the day etc).



Motion sensored room light has been available for at least 15-20 years.


This is billed as a replacement for motion sensors in home automation. Though it does beg the question, "what if someone moves their router?"


This is a great question.

A typical apartment or business has 10s to 100s of routers nowadays that your smartphone can "see" when it scans. Thus, the movement of a single router never really hinders the signal that much.

Still, I might try to add some bootstrapping to the software so that tracking locations can be used to "relearn" places to later test if the routers have been moving around.


Thank you for releasing this, this is a really valuable reference for a project I'm working on.

I've certainly seen urban areas with hundreds of routers around, but where I am it is more like 5.


Your welcome, glad it will help someone.

Certainly give it a try, I've heard that it works pretty well for ~5 routers for a couple of rooms in an apartment.


It adds a lot of complexity and point of failure for a system that I can install for 15 bucks from most hardware stores (with a solid track record).


Yes, but your detector creates more problems than it solves:

* pets set it off,

* it cannot differentiate between different objects in motion. So several people could be moving at the same time and it would only trigger as one event,

* it cannot detect people who are present but motionless (eg watching TV),

* it doesn't remember how many people are present in a room, so you could have 2 people watching TV then when 1 person leaves the detect would think the room is empty,

* it requires multiple detectors,

* detectors are generally visible, which some might find an eyesore (at least WiFi APs can be hidden a little more as fewer needed).

I'm not saying FIND is perfect either, but you have implied that your solution works just as well as FIND and stated that your solution is less complex; which is simply is not true. Your solution creates more problems than FIND and addressing them creates just as much complexity (as I detailed in my other post: https://news.ycombinator.com/item?id=11519159)


Motion detectors have a variety of usage, outdoor lighting, indoor room lighting, grocery store fridge lighting, etc. FIND is a bit more specialized because of the huge drawback of requiring each user to carry a specific device.

I can't use it at my work because we don't all have Android. I can't use it at home because my wife uses in iPhone. Cool idea but limited use compared to motion detectors.


Indeed, but that was never in dispute. FIND was never pitched to replace motion detection sensors to begin with. The argument was whether motion detectors are comparable to FIND for the specific specialised problem that FIND addresses to solve; not whether FIND can replace all the generalised purposes that motion detection is utilised.

My point was always that the two technologies aren't necessarily interchangeable and in an indirect way you're just saying the same thing with your counterargument.


The original comment was about turning lights on and off. You implied FIND is better than motion detectors at this ("your solution creates more problems than FIND..."). In most cases this is false, due to the negatives I outlined above.


I think the confusion here is there's two different use cases for turning lights on and off.

I have acknowledged in another post that motion detectors are advantageous if you're dealing with strangers and/or situations where there's lots of movement and/or lights that can be automatically timed out. eg public spaces halls, public restrooms, security lights, etc. But I don't think it's fair to lump these in the same category as "home automation".

Home automation is a little more of a complex problem as you need the lights in the room to not only turn on when someone enters, but also turn off when they leave. Motion detectors can spot someone moving in a room but they're not to great at detecting when people have left since it's the same sensor that would be triggered. They're also not great at detecting if people have entered a room and are still in the room if those people have stopped moving (eg they are watching TV) - since those people aren't triggering the motion detection. And lastly, motion detection isn't great at detecting the number of people in a room - which matters if you don't want the lights to turn off when someone leaves the room but other people are still in there and watching TV.

Motion detection solved some of the problems of home automation, but creates some problems as well. Which is why I said motion detection is just too simplistic of a solution for home automation despite it being a great solution for other types of automating lighting.

Granted you could place more sensors, network them up, and have a centralised unit logging movement. That would likely work. But then it quickly becomes as complex as the solutions we're trying to avoid.

However even if all these things were easily addressed, motion detection still has issues for me personally as I have two cats. This is the beauty of proper home automation systems: they give you the granularity to personalise things so pets don't set off the same triggers that people do. Or my two year old doesn't trigger the same automation that my wife and I do (eg unlocking the front door). This is where I think the future of home automation lies and is what really gets me excited.

So you're right that there is overlap between motion triggers lights and home automation; but the latter is intentionally a more complex problem by design.


I'm looking at building my own home automation, the PIR sensors are fairly heavy on power and in order to ping them fast enough I need a fairly large battery or hook up the sensor to electricity. If I can replace that with a device in my pocket it would be nice as I don't need extra sensors.

Ofcourse, the downside is if the device is not in my pocket the system has no way to know where I am and will keep the light on in the wrong room and keep me in the dark so it's not like it's a perfect solution.


There are PIR sensors that use no more than tens of microamps of power, and can send an interrupt signal to a microcontroller to wake it from deep sleep. An example is AMN41121 by Panasonic.


I love home automation but unfortunately can't think of any beneficial use-cases. This would require each person being tracked to have an android based device with wifi enabled and the app running.

I can't track my children, I can't track my wife's iPhone. I couldn't even track myself if I left my phone in the charger. It would be neat to track my positioning and run some statistics but I wouldn't say it's useful.


It shouldn't be difficult to assign a temporary trustworthiness score to a given AP that will change if it appears to be in a different location relative to other known APs to factor this in. If it's going to rely on APs not under the users control this will be necessary.



Yeah, but do any of those motion sensor systems detect if a person is still in the room but motionless? Eg if you're sat reading.

I ask because Ive had to wave my arms about far too often in public restrooms due to motion sensors deactivating the lights when spending too long on the toilet. Having that happen in my own home would be annoying enough to warrant the additional complexity of FIND (or ditch home automation entirely)



Yes, but those only detect movement[1]. They cannot differentiate between a motionless person and the rest of the room. Hence my point about the problem with motion detectors in a house given that most people often spend periods of time largely motionless.

There is a workaround to this problem, but it requires adding a networked "intelligence" to the detectors. You'd a detector at every entrance and every exit of every room. Then you'd need to network them up to a server (which defeats the advantage of motion sensors over FIND) and that would log the movement in and out of each room, incrementing the occupancy of the room as it goes along to ensure that lights are not deactivated when two people are in the room but only one exits. By the time you've installed dozens of sensors across the house, networked them, and installed a server, you might as well have just gone with FIND. Not only does FIND require less hardware, it can identify the specific individuals and isn't triggered by family pets (I certainly don't want my cats turning lights on during the night!)

So while you are right that other, simpler, technologies have been around for years, they're simply not good enough for the average home (it still remains to be seen if FIND is, but it's definitely better than motion sensors)

[1] As per the article you cited, details about how the detection on works for objects in motion: https://en.wikipedia.org/wiki/Passive_infrared_sensor#Operat...


Sure, but with this you've got less hardware involved in total, and more flexibility for programmed responses.


I guarantee my ISY-994i and my Insteon motion sensors give me considerably more flexibility than anything that would run on my phone. And that's even when Insteon sucks my will to live.




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