The Truth About “True” Lock-Offs

This article originated in the May/June 2021 issue of Safe Ride News.

A few years ago, SRN reported on an emerging phenomenon: CRs with features that looked and acted like lock-offs but weren’t.

Since then, these features have become more common. Nowadays, CPSTs who see anything that looks like a lock-off ask, “Is that a true lock-off?” While a mechanism that functions as a lock-off must be a “true,” authentic lock-off, “true lock-off” has become part of the CPST vernacular when wondering whether a CR part that appears to be a lock-off actually is one.

This is a good question to ask—relying on a mechanism to hold a CR tight when the mechanism isn’t made to do that job is unsafe! A key determinant is whether or not the feature makes it unnecessary to switch a lap-shoulder belt’s switchable retractor to locked (ALR) mode (or, on an ELR-only belt, add a locking clip) for installation. If it does, the CR mechanism will prevent shoulder belt webbing from redistributing to the lap portion of the belt in precrash conditions. It’s up to the manufacturer to determine if the mechanism has this functionality.

Therefore, consult the owner’s manual (OM) to learn whether or not a feature is truly a lock-off.* But, understand that CR OMs are written primarily for owners; they aim to walk a novice user—not a CPST—through the steps of installation. Therefore, CPSTs aren’t likely to find that the OM directly states whether or not a feature is truly a lock-off, as this would be over the head of most caregivers.

Instead, to learn if a feature is a lock-off, look for instructional clues. One giveaway can be found in the OM’s section on installation using a lap-shoulder belt. Does it direct the user to switch a switchable belt to ALR mode (or, more vaguely, to follow the method for locking the belt stated in the vehicle instructions)? If it doesn’t, then the mechanism must be a lock-off. On the other hand, if the instructions do include a step to switch the belt to locked mode, the device is not a lock-off. Similarly, when instructions for installation using a belt with a free-sliding latchplate and an emergency locking retractor (ELR) call for the use of a locking clip, that’s a dead giveaway that the mechanism isn’t a lock-off.

If such devices are not lock-offs, what are they? The answer is model-specific, and often the CR instructions won’t provide an answer. In some cases, the mechanism is there to keep the belt (usually the lap portion) positioned in a certain place.

Belt tensioners are another category of mechanisms that may or may not also be lock-offs. These mechanisms, which come in an array of styles, have two things in common: 1) They use leverage principles to make them easy to operate while using minimal effort, and 2) they clamp down on webbing in a way that holds just enough webbing slack (seat belt or LA strap) within the CR to ensure a tight installation.

Belt tensioners, now found on a wide range of CR models, have truly revolutionized CR installation because they allow users to get a tight CR installation without the strain of pushing on the CR or tugging hard on the belt or LA strap.

However, always check the CR instructions to learn whether a belt tensioner is also a lock-off; sometimes it is, and sometimes it’s not. Again, the only way to be sure is to look in the OM; if instructions in the section for installation using a lap-shoulder belt with a switchable retractor call for changing to ALR mode, the mechanism is not a lock-off.

Don’t Let Names Cause Confusion!

Like the locking clip that it replaces—which also has the term “lock” in its name—a lock-off doesn’t actually lock a seat belt. When these devices are used, the seat belt still does the job of locking in a crash. A lock-off (or locking clip) simply holds the lap portion of a seat belt’s webbing at a fixed length by preventing shoulder webbing from slipping through a sliding latchplate. This is an important job, as it ensures that a precrash CR is held tightly so it will perform properly at the moment the retractor locks up in a crash. While crash forces may release webbing from either a lock-off or locking clip, at that point, the device has already done its job.

Understanding this functionality helps explain how lock-offs—with their wide variety of shapes, materials, and use—and locking clips can all do the same thing, despite looking very different from one another.
Having a grasp on these concepts is important for CPSTs and helpful when answering some caregiver questions, like “Why does the locking clip have to be installed by the seat belt latchplate?” and “How can this plastic lock-off do the same job as a metal locking clip?”