Some form of compute with a recurring job that checks for a DNS address or domain.
Choose a domain that needs to be regularly paid for as a target.
Reason I would choose something you pay for as the trigger is because not paying a bill after your death is one thing that will be actioned on no matter what.
That’s if they know about it and have access to any of the accounts.
For example you can setup a domain.com account that’s almost completely anonymous.