Abstract: An automatic shut-off valve is used at the inlet point of a fuel line carrying a gaseous or liquid fuel into a house or the like, the valve being adapted to terminate the flow of gas or liquid upon the experiencing of a shock or vibration by the valve as would be produced by an earthquake, with the valve head being so positioned to be actuated by a sudden surge of flow to shut the valve in the event a ruptured gas line causes a quick inordinately rapid gas or liquid flow in the system. The principle utilized to actuate the closing of the valve as a function of a certain minimum amplitude of vibration or shock is a ball weight which in normal use rests on a pedestal which in turn maintains the valve head away from the valve seat in the supply line, this ball being designed to topple from its supporting pedestal during an earthquake or other vibration, thus freeing the valve head to seat under spring tension such as to block the fluid flow.