A seat belt lock-off is a part of a car seat that is designed to hold the vehicle seat belt tight to maintain a good installation. Lock-offs come in many different styles and can be very obvious color-coded levers and latches, or they can be simple clips that don't stand out visually on the car seat.
The lock-off pinches or clamps the vehicle seat belt to create a fixed length of seat belt webbing that holds the car seat securely into the vehicle.
The lock-off helps address the many types of seat belt systems that are present in vehicles today by simplifying the installation process.
Some types of car seat installations may previously have required the use of a locking clip, which can be difficult for parents to install properly. A built-in lock-off can eliminate the need for a locking clip and can increase the ease of use of the car seat. In this way, the ease of use feature (the lock-off) also improves the safety of the car seat because the parent is more likely to use the simpler mechanism properly.
Many car seats have lock-offs on both sides so that they can be used for installation on either side of the car. Other car seats have just one lock off in the center. Some may have separate lock offs on either side of the car seat and for rear-facing and forward-facing installations. It's easy to get confused by all of those clips or latches, so be sure you read the instruction manual that came with your car seat to see which lock off you're supposed to use.
If you don't have the instruction manual, you may be able to find one on the manufacturer's website, or you can call the manufacturer phone number on the car seat label for help.
Car Seats With Built-In Lock-Offs
Pictured is a built-in lock-off on an older Britax convertible car seat. This lock-off clamps the shoulder portion of the seatbelt to create the fixed length of webbing that secures the car seat.
The Chicco Key Fit and Key Fit 30 infant car seats have a very simple but effective lock-off. In fact, they're so simple that you may not even notice they're part of the car seat. On the base of these infant seats, under the top portion of the belt path, there's a thin piece of orange plastic. This piece is attached to the car seat on one end and open on the other end. To use the lock off, you slide the shoulder portion of the seatbelt into the orange plastic piece. There's a lock off on both sides of the base.
The Graco Snug Ride 30/35 also has a lock off on the infant car seat base, but it's a central one that can be used for installation on either side of the vehicle. There are two hinged pieces that fold out. Both the lap and shoulder portions of the seatbelt are routed across the center of the lock off, and both of the hinged pieces are folded over the top. When they click into place, the seat belt is locked down.
Newer Britax car seats may have a feature called Click Tight, which is a type of lock off. There's a part of the seat portion that lifts up like a trunk lid. The seatbelt is routed underneath that piece. When the "trunk lid" is closed again, it functions as a lock off.
The Cybex Cloud Q infant car seat has a similar hinged lid piece on the car seat base.
Because there are so many types of built-in lock-offs, parents should always read the car seat instruction manual carefully to learn how to use this feature. Some car seat manufacturers allow you to lock the vehicle seat belt while using the car seat lock-off, while others do not. Again, be sure you read the car seat and vehicle instructions to ensure you're using all features correctly.