Check-in simulator Prototype
A time-lapse of what the check-in switch is meant to do. Days speed by. First the owner checks in on schedule. Then you can make them go quiet and watch each warning fire, until the locked letter would be released. Or press False alarm to see how a single check-in stops everything. Nothing is sent. This is a model, not a live service.
Using the settings from your plan.
Day
0
What happened
The letter has been released, but the heirs still can't open it. They need k of the shares you handed out. If this were a mistake, the real service is designed to warn the owner many times and ask a trusted person first, which is why release is the last step. Try the heir claim.
The false-alarm button works until release. After release there is no undo, which is why the grace period is long and the earlier steps use more than one channel.