For many years, a locking clip was used to lock all lap and shoulder belts when installing a car seat. This was the only available method for locking the belt. Today, there are a number of other options available.
Since September 1, 1996, all American cars have been required to have seat belts that lock before a crash. This feature is solely for car seat installation. How they do that was left up to the car manufacturer, and so they lock either with a switchable retractor at the shoulder, a locking latchplate, or a switchable latchplate.
Cars that don’t have belts that lock before a crash (cars which require locking clips for car seat installation) are now over 18 years old. With these cars aging off the road, locking clips are becoming less and less common. Evenflo and Dorel have stopped sending them with new seats.
The big reason is to prevent tipping. When a lightweight (and occasionally heavy) seat is installed with a locked shoulder belt, every bump in the road can cause the belt to lock a little tighter. After either a few hours or a few weeks you end up with a child who is looking out of the side window rather than up toward the ceiling. By using the locking clip, the shoulder portion is left unlocked and thus the seat does not tip.
Another reason for using a locking clip is when a belt that locks at the buckle doesn’t lay flat properly and stay locked. A lightweight or heavy-duty locking latchplate loosens when you lift the buckle and tilt it. If the belt isn’t laying flat and the buckle is lifted, the seat belt will stay loose. Sometimes a locking clip is used here to keep the seat belt locked properly, even though the belt itself locks. Not all combinations of seating positions, seat belts and car seats produce a functional installation: a locking clip can solve this.
For some people, the only time they will use a locking clip is when traveling internationally. The United States is the only country to require lockable seat belts. The rest of the world does not require pre-locking belts.
If you rent a car, depending on where in the world you are, it may have ISOFIX (lower anchors, and maybe a top tether). Your options then for a rear facing seat are lower anchors or a seat belt with locking clip.
Locking clips are NEVER used on a lap only belt. If a lap only seat belt does not lock, please contact a certified technician or even a technician instructor for assistance with your installation.
Some car seats come with built-in locking clips called lock offs. If a seat has these, read the instruction manual on when to use them. Some require one, some two, some with the seat belt only, some all the time. These seats usually do not come with a separate locking clip.
If your car seat did not come with a locking clip and you have a car seat that tips or are planning to travel internationally, please contact the manufacturer of your car seat. They should send out a locking clip. You can also use one from any seat as they are interchangeable standard equipment.
While you can use a locking clip on any lap and shoulder belt with latch plate that slides, they are often not necessary and can be misused. You may hear technicians groan when a locking clip is brought out. While they are a wonderful solution to a problem, using them can be complicated and when misused, can be very bad for the child in the event of a crash. This is a video of a locking clip that has been placed on the wrong side of the seat belt:
If you feel you need a locking clip because your belts don’t lock properly, or you have a seat that tips, please read your manual, watch videos about installation such as the one below or find a local technician or instructor for assistance. While locking clip installations aren’t necessary most times, it does happen and it needs to be done properly.