This is likely to be our Top Pick winner for best lightweight locking carabiner. It only weighs 42 grams!
It's other superlight competitors are hard to find. The Wild Country Neon Keylock Screwgate and the Mad Rock Super Tech Keylock Screw appears discontinued.
For being such a light wiener, it is relatively large and easy to handle. The key lock gate and rounded angles inside the biner make it easy to get on and off bolts and webbing.