[spookylettuce]

My child is old enough now to stay home alone during short errands. Since we don't have an old school land line it would be cool to take inspiration from a project like this and build her a "red line" device that gives her immediate access to reach me without breaking down and buying her a cell phone yet.

But what would I hack together for the software side of that?

[asciimov]

I'd skip the projects and just buy one of the numerous phones that target this market. They make watches, dumb phones, and smart phones, that are locked down and only allow phoning/texting specific people.

The other option would be to get a real copper phone line.

My reasoning is that a real emergency may include a power outage. Relying on some cool hack isn't going to be helpful when your child is trying to reach out to you when there is no power at home.

[alerighi]

Unfortunately in my country even landline phone lines don't work on power outages, since with the transition to digital only lines (with VDSL) is the router that inside has an ATA to which you connect your landline phone. In fact you have VOIP phone service at your house (in fact you can avoid completely to connect your phone to the router phone socket and use whatever VOIP phone you want, with the correct settings extracted from the provider router).

Even if you provide backup power to the router is not enough, since at the other end, VDSL cabinets in the street, there is no backup power, so if it's not a blackout of only your house but it insist the local transformer, the VDSL cabinet is probably out of power too and thus no line.

The only reliable solution is 4G that is not so reliable since in case of emergency lines get overloaded.

I probably should get an ham radio license to be safe...

[kalleboo]

I bought a Cisco SPA112 ATA (VoIP analog telephone adapter) off eBay for under $20 to use with my retro computers, and for my kids I picked up two analog phones at a junk store and set it up to allow dial through to the other one, so my kids could call each other (sitting right next to each other) for free.

The same device can also be configured to use a VoIP provider and with all the configurability of it I bet you can get it to auto-dial when you take the phone off the hook. edit: it looks like yes it is doable https://community.cisco.com/t5/atas-gateways-and-accessories...

[jareklupinski]

The simplest solution for me was to get a "feature phone" that doesn't have apps or anything else enticing, and leaving it in the drawer as an 'emergency phone'. The SIM is on the family plan so it's not a significant expense, and it keeps a charge for about a month as it's off most of the time anyway.

It ends up not becoming the emergency phone and more 'remind xyz to grab abc on the way home' phone but oh well :)

[squarefoot]

If you are within short range radio coverage, why not walkie talkies?

Check PMR446 (EU), FRS (US) and similar services.

https://en.wikipedia.org/wiki/PMR446

https://en.wikipedia.org/wiki/Family_Radio_Service

[bellyfullofbac]

If only Whatsapp/Signal/Telegram has open APIs to allow voice calls...

But I guess using VoIP software it's not a new idea: https://github.com/hnesland/aselektriskbureau

It would be neat to enable dialing, e.g. "1" for Mom, "2" for Dad...

[alerighi]

You can buy an ATA (Analog Telephone Adapter) to convert old analog phones to VOIP, and then use it with whatever VOIP service you want. Just be sure that the adapter supports pulse dialing since you want to use it with a rotary phone (not all does).

[wolfgang42]

If it’s being used as a “red phone” (pick it up and it immediately calls the other end), the feature that the parent wants to make sure it has is is “automatic ringdown”.

[opencl]

The software could be pretty simple. Hook a button up to GPIO, write a bash wrapper around one of the command line VoIP clients, write a little program to call the script when the button gets pressed, autorun that one on boot.

[bombcar]

If you’re in the Apple ecosystem the homepods can intercom.