PIR sensor behind glass?

yo-less

Hey everyone, as I’d like my mirror to look as mirror-like and non-electronic as possible, I would like to hide the PIR sensor but after some initial tests it seems like putting it behind the mirror glass is not going to be an option. If you have managed to hide your PIR sensor, how did you go about it?

strawberry 3.141

it will not work behind glass but @alexyak wrote a module for webcams or pi cams to detect motion, which can be hidden behind glass https://forum.magicmirror.builders/topic/490/motion-detector

yo-less

Thanks man, I am aware of that module, but I’m reluctant to install a webcam in my home that is connected to the internet.

strawberry 3.141

well you could put your sensor outside of the mirror and hang it into a corner, so it’s not obvious that it belongs to the mirror itself

yo-less

@strawberry-3.141 As of now, that would probably be the best option. I’m curious as to what other mirror builders may have done to hide the sensor.
I’ve tried to find other sensors, such as radar motion detectors, but haven’t yet found one that I could easily attach to my Pi.

If someone has a radar motion detector or a different way of detecting motion (other than using a webcam) already implemented into their Pi setup, I’d be very interested in finding out more about it.

Can a PIR sensor be covered by anything at all or does any kind of material automatically block motion detection?

Knox

@yo-less said in PIR sensor behind glass?:

Can a PIR sensor be covered by anything at all or does any kind of material automatically block motion detection?

Technically the sensor is covered by something, but that thing is the focusing Fresnel lens. Depending on the PIR you got, you’ll notice the plastic domed lens does come off rather easily.

“These curved segments are Fresnel lenses which constitute an array that increases the detection zone of the sensor. Fresnel lens array is known to capture more infrared radiation and focus it to a relatively smaller point. Detection is more stable and maximum distance for detection is also increased. Fresnel lens has been crafted to be translucent so that it can capture only infrared radiation without getting unwanted radiations from visible spectrum of light.”

Now the issue is that most glass and metals reflect IR wavelengths extremely well. So depending what the film/mirror backing is made out of may make your efforts mute. Aluminum which is used in most standard mirrors reflects all of the Infrared light in the spectrum.

So mounting it behind the mirror just doesn’t seem practical due to the way light works. So what I’m thinking of for me, is to mount it in a light fixture above the mirror. Not sure on the details yet but that’s where I am right now.
However the Camera trick does function very well and will give you that clean look.

yo-less

@Knox Yeah, thanks, my Fresnel lens isn’t even fixed to the PIR sensor and comes off right away if you don’t find some way of keeping it there ;-). But you’re right, didn’t think of that, it’s actually covered by this plastic dome. Maybe if I install the PIR sensor in the frame of the mirror and cover that section of the frame with acrylic glass, such as Plexiglas, it might work and look alright. Will try and test if my sensor detects IR behind a sheet of acrylic glass.

Knox

that would be a good test, but just note you’ll be lowering its effective area. Which for a mirror might be fine, as you normally stand directly infront of it.

yo-less

Sure, I guess I’d have to play around with its sensitivity, will keep you updated on the outcome of my tests

RedNax

Pir isn’t really an option behind glass. There’s a cam based solution which works through the mirror.

That said, my mirror is full sized and the pir peeks out the bottom… You’d never know it’s there unless you know where tot look…