Carabiners having locking systems of the type called “key-lock” for mountaineering and climbing are provided. Such carabiners include those having a ring with a side, interrupted by an opening delimited by a first and a second end, wherein said opening is closed by a spring closing element which can take an open position and a closed position, wherein the first end of the ring comprises a bulb-shaped hooking portion, with the projecting part in a direction transverse to the plane of the carabiner, wherein the coupling portion on both sides of the bulb includes a shoulder having an uneven surface.