Abstract: A deceleration sensor for detecting a threshold level of deceleration indicative of vehicle crash, comprising a sensor mass, a spring-loaded firing pin received in a guide bore, a trigger lever for engaging the firing pin in a dormant state until the trigger lever is disengaged from the sensor mass as a result of the occurrence of a deceleration in excess of the threshold level and the resulting inertia motion of the sensor mass, and a safety catch which may include a rotary shaft extending perpendicular to the plane of the inertia motion of the sensor mass and a part of a front end portion of the guide bore, the rotary shaft being provided with a first notch and a second notch which, respectively, permits and prohibits the propulsion of the firing pin through the guide bore by aligning with the guide bore.