Abstract: A passive safety device comprises a sensor unit for determining vehicle accelerations and decelerations, an evaluating unit for evaluating the output signal of the sensor unit, and a triggering unit for the activation of an occupant protection system upon the reception of a trigger signal, to protect the occupants from injuries. The individual units of the safety device are connected by way of optical lightguides, i.e. the communication among the individual units takes place through optical light signals. The sensor unit has an optical-mechanical acceleration sensor with at least one input lightguide, light being transmitted to the acceleration sensor by way of this lightguide. This light is transmitted within the acceleration sensor to at least one output lightguide. The optical system of the acceleration sensor arranged between the two lightguides is exposed to the accelerations to be detected and changes its optical properties in dependence on the magnitude of the acceleration forces.