Carabiners with a straight gate may have a locking mechanism that makes the carabiner safer to use, as the risk of the gate opening at an inappropriate time is removed. Locking mechanisms can be both manual and automatic, both with their own advantages and disadvantages, for example, you still need to remember to check if an automatic lock is closed properly. Carabiners with a locking mechanism are used to secure with and when safety is critical.
A screw-lock is a manual lock that works by screwing a cover over the top of the gate and the carabiner opening, thereby preventing the gate from opening. As this is a manual lock, it is important to check if it is locked every time you use it.
A twist-lock is automatic that requires two movements each time it needs to be opened. First, the sheath over the gate must be rotated, often 90 °, and then the gate will be opened. When the gate is released again, the gate closes and the cover rotates to the locked position automatically. Twist-lock is simple and quick to use and means that you do not have to manually lock the carabiner every time. On the other hand, do still remember to check the carabiner every time.
Tri-lock is a variant of twist-lock that requires the third movement before the other two, of which “tri “comes from. The third movement that must take place before the other two, is that the cover that sits over the gate must be pushed up, after which it can be rotated and the gate can be opened. Like the Twist-lock, the tri-lock also locks automatically when the gate is released. The extra movement makes the tri-lock safer than the other two but is also a bit more inconvenient.
A pinch lock is a relatively rare lock where you have to press a button on each side of the gate before the gate can be opened. A variant of pinch-lock is botton-lock, where there is a button on the inside of the gate that must be pressed in before the gate can be opened. Both lock types are automatic.