[safety1st]

Simple, use a dead man's switch. The simplest form being some kind of data access which can be set to expire, and the expiration date can only be extended by you.

[Kathula]

Simple for the audience on HN perhaps but not for the non-technical everyday person.

[safety1st]

A conveyor belt with a button that needs to be held down for the belt to run, is a dead man's switch

A Google Drive folder which has a sharing policy set to expire in 30 days, is a dead man's switch

You don't need to be technical to use a dead man's switch.