I know this doesn't meet the parameters of FOSS, but in this instance I'd discard privacy concerns and just get her an Echo or Google Home. They're cheap, and bring able to call out a help request is better than a button she can forget to carry or wear. Either is capable of hearing a command in a 2br apartment, and have SOS ability.

I have a failing MIL in a similar situation. She's living alone, isolated, not near any family, and won't move. I gave her a Google Home I had in a box from a few years ago, and it is a godsend. She talks to it, it talks back, and she can make it do things she's not capable anymore of doing with technology. But most importantly, she can call any of us by telling the Home to do so.

I wouldn't risk a cobbled-together solution, personally, and right now the OSS technology stack for voice recognition is (a) not inexpensive, and (b) futzy. I have no doubt it'll get there; there are already some promising devices, but that integration with calling and SOS is the key.

Edit: typos

It doesn't help that there is a dog living with her (I'm not gonna paint the picture, but I'm sure you heard the stories...).

FWIW I think you're thinking of cats. A loyal dog will often starve to death before harming their master.

All that being said, I think this is one of those hills where it's not worth dying on for FOSS. There are services out there that are designed to do this and have round-the-clock monitoring. Do you really want to trust that your jury-rig solution is fool proof enough to save her? As you said, if you are out of the house, it does no good. Just something like lifealert is probably better here.

Foss has its uses, this isn’t one of them. Get her a life alert or other fully supported solution as this is something her life could depend on and it’s not worth the risk

Just commenting to say how nice it is of you to be that caring about your neighbor.

You want something that she's comfortable with. A necklace or a bracelet/watch with a big red button that's also specifically made so you don't have too many false alerts. Because that happens all the times. People do chores and push the button inadvertently and older people don't want to bother people, so then they're ashamed of having too many false alerts and won't have it with them 24/7 out of false shame. So use something that's made for the purpose and not a doorbell.

Also it has to be obvious how to use it. Even when in distress at 5am after you've fell down and can barely remember what you're supposed to do. A necklace with one big red button will probably do it. Or something similar she can wear around your wrist.

There are also emergency phones with a red button on the back. (And watches with fall detection.) But you need to have a subscription for the phone to dial out. And it needs to be charged regularly. A RF button won't have those downsides.

I don't know which product to buy. But seems there are several ones out there < $50

Search keywords would be something like: elderly, emergency button, necklace, pendant, alert system, call button.

https://www.pflegerufset.de/ELDAT-RS16-Hausnotruf-mit-Armbandsender-mit-Quittierungssender/PRS10125

https://www.rollstuhl-senioren.de/hausnotruf-fuer-senioren/

https://www.amazon.de/-/en/Emergency-Seniors-Bracelet-Monitor-Elderly/dp/B0B6VRN8JF/

https://www.amazon.de/Handsender-Hausnotruf/s?k=Handsender+Hausnotruf

https://www.tuerklingel-shop.de/Mobiler-Alarm-Notruf-Knopf-Funk-Senioren-Hausnotruf-Pflege-Ueberfall-2-Sender-Pflegedienst

Aliexpress also has some "Tuya Wifi Smart Sos button". But I'd probably go for something simple. A button that sends a RF signal and a receiver at your place that's making the audible alert. WiFi, bluetooth, Apps etc make it more complicated and more likely to fail.

Thanks for you answers so far.

My point is, she is still mentally there (I think) so if she wants one of those subscription buttons, she can 100% get it herself.

I was just thinking, as an extra layer of security, if I'm in the area to help out.

As others have said, just buy a ready made solution. There's several options without a monthly fee and no smartphone app. Hell even at RadioShack 20 years ago there was an option that tied into your home phone system.

Try googling "emergency dialer" to find good examples.

Here you go. Will do specifically what you want, including Web hooks and MQTT out of the box. The Shelly cloud is fine, but these are flashable with tasmota or esphome or roll your own firmware.

https://usa.shelly.cloud/knowledge-base/shelly-button-one/

I have a number of these buttons about the house

SNZB-01 https://www.ebay.co.uk/itm/304860775879?mkcid=16&amp;mkevt=1&amp;mkrid=711-127632-2357-0&amp;ssspo=fzhcellmt0u&amp;sssrc=2047675&amp;ssuid=hddZAAubQsK&amp;var=603868193820&amp;widget_ver=artemis&amp;media=COPY

I have a RasPi running https://www.zigbee2mqtt.io/

I have one of these flashed as hub / bridge https://www.ebay.co.uk/itm/203668277433?var=504097716478

Then just some python connecting to the mqtt and responding which I'd be happy to provide a copy of if you decide to go down that route, just let me know. Could have it sending a pushover notification or something along those lines quite easily

Look, what about an Amazon Echo? I know it's not open source at all but depending on the house size a couple Echo Dots could cover a lot. I think they can make phone calls because I've called my phone to find it before with mine but I'm not sure.

A benefit is that she won't have to have it on her person.

Something like a Ring Doorbell could work too. Just thinking out loud. This is a weirder suggestion. They have a battery and nothing says they have to be installed on a wall. Just turn off motion completely. At that point she can press the button and talk to you.