A safety device, of the anti-false maneuver type, capable of impeding the actuation of a locking fitting upon opening of a leaf of a door, window or the like, this safety device including, on the one hand, a support in the shape of a casing capable of being inserted against a face-plate and, on the other hand, a locking finger passing through this latter, under the action of springy restoration means, with a view to locking an actuating rod in translation, this when the door or window is open. In particular, the casing defined by the support and serving as a housing for the locking finger includes, at the level of each of its opposite sides parallel to the plane of the leaf on which it is fitted, an opening serving for the passing through of the connecting lug which is capable of being fitted onto the locking finger with a view to actuating same under the action of an actuating lug extending.