I know some disabled or ill people have some kind of ‘red button’ device that they can hang around their neck to use to call for help.
I wonder if I could get such a thing myself? The ideal would be some button thing that could plug into my iPad via a cable into the lightning port. If this could then use the WLAN or even the internet to summon help from Janet’s iPads and iPhone then that would be perfect. If she is across the field, it would be a matter of going outside of the WLAN into the internet and across to 4G-land to get to her iPad or iPhone on either EE or AA on the internet.
Devices that rely on a single physical layer connection all the way to my beloved would not be good. It would need to capable of being L3-routed as the circumstances require. Being guaranteed to be able to work across the local WLAN alone would be a big plus, so that if there is no router or no internet access then things would still work. Easy, as at L3, devices could optionally use link-local addresses (or Mac addresses?) whilst we are on the same broadcast subdomain, which is the case while she is in the house. But however it is done, we also use global, routable IPv4 and IPv6 addresses throughout to make things as easy as it could possibly be.
