A switch including a mass suspended above a base by a flat horizontal spring has electric contacts that close in response to the initial shocks of major earthquakes and activates safety devices before the onset of destructive ground motions. The vertical unidirectional seismic switch can be manufactured by micromechanical photolithography and is integrated with electromechanical safety devices to latch cabinets closed, secure movable objects, shut off gas, water, and electric utilities, activate alarms, early warning networks, and related automated response systems. The device is fully self contained, consumes no power until activated, is inexpensive to produce, and impervious to nonearthquake noise in that it is designed to respond specifically to the vertical acceleration and displacement characteristic of the initial shock waves of a major earthquake.