The other problem is which people are likely to install the app. It basically requires a modern Android or iOS smartphone with internet connectivity, which probably excludes the really at-risk groups that are of most concern: https://www.dw.com/en/loved-or-loathed-how-germanys-coronavi...
So, elderly people are less likely to use a smartphone (though I suspect not THAT much less likely). But the people they come in contact with probably do use one, mostly. Generally these should work on any smartphone under five years old.
Trying to create hardware token for this. Because myself and many friends are not able to use this. And if I think of old people not able to handle smartphone, this should be useful.
https://github.com/Lurkars/esp-ena
