Abstract: A sensor for activating a vehicle occupant restraint system, in particular the locking mechanism of a safety belt retractor, has an inertia body, a bearing on which the inertia body rests, and a sensor lever arranged in an upper region of the inertia body. The sensor lever can be swiveled from a position of rest by a movement of the inertia body and thereby activates the vehicle occupant restraint system. The inertia body in a position of rest is spaced apart from the sensor lever by a gap or, in the position of rest, it contacts an abutment surface of the sensor lever in exactly one point and is spaced apart from a jacket surface of the sensor lever which adjoins the abutment surface.