Abstract: A seismic alarm device for vehicles which is capable of detecting an earthquake while the vehicle is moving and gives the alarm upon occurrence of the earthquake in order to provide the safety such as by stopping the motor vehicle, wherein a plurality of acceleration detectors are mounted on the front and rear of the vehicle or on the left and right sides of the vehicle, output signals generated from these acceleration detectors are fed to a determination circuit, which determination circuit is arranged to measure an amplitude and period of the output signals and to compare phases of the output signals, then to output an alarm signal if the amplitude of the output signals is larger than a predetermined value while their periods are within a predetermined range and no phase difference exists between the output signals of the acceleration detectors, and an alarm circuit gives the alarm when the determination circuit outputs the alarm signal.