If you have been considering a device like this, would you use a modern pager?
https://en.m.wikipedia.org/wiki/Pager
The idea is that you could (say) send your aging mom occasional unobtrusive messages. Big letters would help. And they could do likewise, via some sort of keyboard.
Needs to be drop-dead simple. If it's cheap enough, maybe no "addressing" at all--the messages always go to a single correspondent.
My aging parents can no longer deal with texting or email. Even voicemail has become too much.
I think a lot of people already have a "pager" in the modern era, and it's a smartwatch. Samsung even sells a 4G smartwatch that doesn't need the phone nearby to operate, and that would give you the rough functionality of a "pager" in a better, modern form factor.