Abstract: An automatic circuit breaker for a vehicle, such as an automobile, truck, boat, airplane, or the like, having an internal combustion engine with at least one associated electrical power circuit which includes a switch in such power circuit together with a toggle joint operative to open and close such circuit and a pendulum-like weight adapted to move upon vehicle impact to actuate said toggle joint to open the switch, thus to avoid electrical ignition of the gaseous fuel subsequent to a gross impact of the vehicle. The same impact can be arranged to actuate the toggle joint to either open to close other circuits.