Abstract: The invention relates to a device for locking a part (3; 21; 31) that is to be secured, arranged so that it can move on a motor vehicle, a securing part (11; 26; 36) engaging in a slot-shaped cavity (7; 28; 38) of the part (3; 21; 31) that is to be secured under the effect of the acceleration forces that occur when the corresponding vehicle coincides with an obstacle. To allow the device to be fitted simply and in a non-bulky way and to reliably prevent unintentional opening of the door of the vehicle when acceleration forces from different directions are applied on the part that is to be secured, the invention proposes that the securing part (11; 26; 36) be controlled by a control element (10; 22; 32) of spherical shape, the control element (10; 22; 32) resting on a guide (8; 23; 33) via domed or conical control surfaces (9).