A spring loaded pin blocks the closed gate's opening path at the location where the gate's opening end engages the carabiner body. The spring serves to normally position the pin so that a portion of the pin protrudes into the opening path of the gate thereby blocking its movement. An open gate pushes the pin aside as it closes. Alternately, the spring can be replaced with a friction member that holds the pin either locked or unlocked when the gate is closed. The gate is unlocked by using a finger to manually push the pin out of the path of the gate end. Although ideally incorporated on wiregate carabiners, the inventive locking mechanism can also be adapted to block the opening end of both straight and bent rigid gate carabiners.