Motion sensor that can "see" through glass

That might work, but it's a lot of hassle and complication. The doorbell already is an electric signal. Could you not use that directly?

-- /¯\ No | Dipl.-Ing. F. Axel Berger Tel: +49/ 221/ 7771 8067 \ / HTML | Roald-Amundsen-Straße 2a Fax: +49/ 221/ 7771 8069  X in | D-50829 Köln-Ossendorf

I did that. I bought a wireless doorbell with two "ringers"; one is in the hall in conventional use, the other is hooked up to an old BeagleBoard that had become spare. I found that the electronics could be powered from 5 volts, available from the BB, so it didn't need plugging in to the mains - fortunate, as the power supply is a non-isolated type.

I wrote some software to send a message to Pushover, which sends me an alert on my mobile phone. It usually arrives within 2 seconds, but it has to be admitted that occasionally it takes much longer, so it's definitely not ideal.

The same idea can be used with a conventional doorbell. It's just a case of appropriate interfacing.

As for why: in our house, if we're in the sun lounge, the ringer in the hall is completely inaudible. Same applies if we're in the garden. There are other places where we can be, and the sound of what we're doing can drown the doorbell. So it's a different use case, but it boils down to the same thing.

If anyone knows a way to get notifications to a mobile phone that are always timely, I'd like to know.

David

I have purchased (through AliExpress) a number of RCWL0516 "Doppler Microwave" motion sensors that provide (among other things) a single-bit binary interface suitable for use with one of the Raspberry PI's digital pins.

As the device uses weak microwave radiation, it can sense motion through glass, brick or drywall, and has an adjustable range of up to 5 metres (about 15 feet) depending on the intervening media.

These devices typically cost less that $1.00 (excluding shipping).

Perhaps one of these would work for you.

Heh! You don't know about my doorbell. It's a brass replica of an antique. You twist a knob on the outside of the door which spins a clapper against the bell on the inside. No electronics, or even electricity involved.

I'll explore that option then. Might be an amusing winter project. It also occurs to me that there may be some Arduino peripherals that can output some relatively loud noise. I may be able to forego the Pi altogether. Thanks for the quick response.

Correct. In that case I modify my suggestion and suggest that a microphone with some very simple electronics right next to the clanger is simpler and more relible than anything optical.

-- /¯\ No | Dipl.-Ing. F. Axel Berger Tel: +49/ 221/ 7771 8067 \ / HTML | Roald-Amundsen-Straße 2a Fax: +49/ 221/ 7771 8069  X in | D-50829 Köln-Ossendorf

You might want to look into the doorbell units sold at this link.

No, I have not used the product myself.

Look at Andreas "guy with the swiss accent" Spiess on youtube, he has videos on various sensor types, including radar type, and connecting to rPi and microcontrollers.

e.g. this playlist, but search his channel for more ...

I would be inclined to think in terms of burglar alarm sensors.

Yes, I was going to say that microwave as opposed to infrared (PIR) motion sensors work through doors, windows, etc.

Over here (UK) the DIY sheds have both PIR and microwave sensors available quite cheaply.

Easy to set up initially but might be very hard (fft) if it has to distinguish the bell from other sounds, if those are about the same level. So I'd be inclined to fit a microswitch to the bell mechanism. Easy, direct on/off signal but probably a little more finicky to set up.

I disagree about the reliability. Sound decays with the square root law. If you place a microphone right nexr to the source it will be hard to confuse it with an external equally strong signal anf if that happens it should be obvious.

You can get a mechanical switch to be reliable for a long tinme, but it's hard.

The suggested optical (or microwave) slution will be the least reliable of all, I expect.

Assuming you already have a "push" doorbell on the outside, can you not attach a lightbulb in parallel with the inside ringer? Alternatively

Use a short range proximity photocell pointing at the clapper mechanism, then an arduino to monitor *change* of state, so it doesn't matter if the mech stops with the photocell obscured or not. Something like this:

Use two of the arduino outputs in antiphase at (say) 2kHz to directly drive a ceramic sounder.

Done this sort of thing loads of times :)

On Thu, 23 Dec 2021 21:53:27 -0000 (UTC), Chris Schram snipped-for-privacy@me.com declaimed the following:

Not really surprising -- it's one reason car and home interiors get warm when the sun shines on glass. Ultraviolet light passes through glass, gets absorbed by fabrics and what-have-you on the inside, and those items then re-radiate the energy in the infrared band.

Sorry -- ultrasonic sensors will reflect off the window itself. You'll pretty much have to fit the sensor (for almost anything except image processing type detection [this image differs from last image]) outside the window and run leads to the R-Pi (or whatever you use to process data).

A PIR sensor /might/ be usable in daylight (they are commonly used for auto-activation motion detect security lights). They trigger on an IR source moving between segments in the sensor window.

Ultrasonic wont see through glass or the clear lid of an electronic box, (I did check to be sure). So it would need to be mounted externally, and then you have the problem of weather proofing.

---druck

There are waterproof ones available, I bought one to use as a tank water level sensor and the sensor is completely sealed up. Then again the same applies to IR solutions, so one has to assume the OP just doesn't like electronics outside.

I didn't see anyone mention mounting a laser pointing at a slightly-angled mirror outside which reflects the beam back to a light sensor. Just one more option, so long as it can be mounted at a height where people won't accidentally look into it.

I've got a Raspberry Pi B with a Pi Camera mounted and use the 'motion' package to record video when motion is detected - through a window. Video is not very high quality, but you don't need that. You could use inotify to watch the destination directory and email you when motion is recorded.

I've just tried it - yes it does work. The only problem is the email delay if your email program doesn't pick up quickly.

Run this file from /etc/cron.d/inotify @reboot root /root/bin/inotify

#!/bin/bash #/root/bin/inotify sleep 10 inotifywait --quiet --recursive --monitor --event create \ --timefmt "%A %Y-%m-%d %H:%M" --format "%T %e %w %f" \ /home/pi/pics | \ while read change; do mail -s "Motion video event" snipped-for-privacy@osmc-3plus.local <<<"$change" done