an electro - mechanical impact detecting device for a vehicle is provided which implements a multi - stage control for vehicle occupant protection systems and improves the operational delay characteristics of the vehicle occupant protection systems at an irregular collision based on the setting of multiple impact levels which are detected . when a main rotor rotates by a certain amount against the exertion force of a moving contact , the moving contact and fixed contact close the circuit , thereby detecting the first impact level . when the main rotor further rotates against the exertion force of the torsional coil spring , the remaining two pairs of fixed contacts and close the circuits sequentially , thereby detecting the second and third impact levels , respectively .