deadswitch
nounUK /ˈdɛdswɪtʃ/
US /ˈdɛdswɪtʃ/
A deadswitch is a special button that makes something stop or turn off if a person lets go of it.
The train driver holds the deadswitch so the train stops if he falls asleep.
OTHER MEANINGS
2. A device that automatically shuts down a machine when its operator is no longer able to control it.
The robot's deadswitch turned it off when the worker stepped away.
3. A hidden switch used to disable an alarm or security system.
The guard used the deadswitch to silence the alarm during the drill.
4. A switch that stays off until someone presses it again.
The deadswitch on the toy car keeps it from moving until you press it.