Almost all new child safety seats have a metal clip attached to them, called a locking clip. A few child safety seats have built-in locking clips, called lock-offs.
A locking clip is used only to keep a certain type of shoulder/lap seat belt locked during normal driving conditions. It cannot be used on lap only belts!
The type of seat belt that requires a locking clip does not lock at either the retractor (the part of the seat belt that winds up excess webbing) or the latch plate (the metal part of the seat belt that clicks into the buckle) during normal driving. If the belt is not locked sufficiently, the car seat can be out of position in a crash resulting in potentially serious injuries to the child.
Before deciding whether or not your seat belt needs a locking clip, read your vehicle owner’s manual to learn how to lock your seat belt when installing a car seat. If your seat belt needs a locking clip, read your car seat instructions to learn how to attach the locking clip to the seat belt.
If you have a car model year 1996 or later, you might not need a locking clip. Seat belts manufactured beginning in model year 1996 cars are required to meet a “lockability standard” and have a method to lock seat belts with car seats.
Lock-offs are built in features on some car seats that lock seat belts in a similar method as locking clips.