Dead Man's Handle

One might have heard of a dead man's handle. There are more fashionable expressions now, which omit the word "dead". Some forms of dead man's handle I have come across through the course of my ministr(ies). Originally, it was a handle which a train driver pushed intermittently to prove that he was still in control. If he expired, the train pulled to a halt. But there are various situations where a dead man's handle -- of sorts -- is used. A more sinister one is that used by terrorists. Harm the terrorists, and your hostages are dead or your headquarters destroyed. A common use is to ensure that an operator is still on the job -- for instance, when pumping water from a mine. There are other, more "conceptual" forms of dead man's handle. For instance, take an informant out, and his information goes public. Or terminate an employee, and the company's mainframe goes down.