Of you already have a will the most secure, proof idiot way I’d to add that key + instructions to the will. Get some lawyers on board for that and it will work.

If you still have concerns about having the full key on a single place, add a topt or second way of identification and distribute it between your heirs.

Sometime, the old fahion way is the best one by far.

Fritzbox boxes.

They tick all the checkboxes

• good standards support (including dect protocol if you want to have an ip phone or even iot protocols)
• fast wifi speeds
• cheap (at least for the second hand in ebay)
• super stable, never had a problem with them in 5 years or more
• fast roaming support out of the box

It is a well known brand in Germany but pretty unknown outside that country. Honestly it is the best bang for buck I was able to get.

Honestly, I would spend 10 minutes checking on them