The hardest part would be how to trigger the kill-switch periodically without showing it to your adversary whilst keeping it easy. Having your device queried directly would be a dead giveaway. My idea without involving people would be as follows:

1. Set up a program that syncs files to a remote third-party cloud
2. Sync it to a directory that frequently changes when you use your device (your docs, for example)
3. Have a server that queries the third-party drive for that synchronised directory
4. If there are no changes, trigget the alarm

But since this plan relies on the secrecy, it’s kind of ruined now. That, and I think your threat model is a bit too extreme.

A dead man’s switch doesn’t quite protect you from garden hose cryptanalysis though. Nothing stops them from asking you to tell them if he got a dead man’s switch.