Abstract: A weight member is supported from an associated vehicle side door for generally horizontal oscillation of at least a major portion of the weight member along a path extending in a front-to-rear direction relative to the direction of intended movement of the vehicle. The vehicle door includes a vertically shiftable door latch lock actuator shiftable between upper and lower active and inactive positions, respectively, and motion transmitting structure is provided and operatively connects the major portion of the weight member to the lock actuator for downward shifting of the latter from an inactive position to its active position in response to inertia shifting of the major portion of the weight member in a forward direction relative to the direction of intended movement of the vehicle.