Dead Man's switch is a time based logical bomb script which executes a certain function if the supposed owner of the script fails to interact the terminal (Could be modified to entering right password for security of the switch).
A dead man's switch is script or compiled binary file that has certain function in place to run if the owner of the script or binary file doesn't interact with terminal or enter the right password in, within a certain period of time such as 6 hours, 24 hours, 3 days etc. When the owner interacts with the running script, the timer is reset.
Have fun.