What feature must be present for a switching retractor to be effective?

A switching retractor is designed to enhance the safety of child restraints by locking the seatbelt in certain scenarios, such as during a crash or sudden stop. For a switching retractor to function effectively, it must switch to a locked mode at the appropriate time. This locking mechanism prevents the seatbelt from retracting or loosening, ensuring that the child restraint remains secure in place during an impact or abrupt motion.

The ability to transition to a locked mode is crucial because it directly impacts the effectiveness of the child safety seat in protecting the child. If the retractor does not lock when necessary, the seatbelt could allow too much movement of the restraint, increasing the risk of injury to the child.

The other options, while they may involve aspects of seatbelt technology, do not directly address the critical feature of locking during an impact, which is central to the effectiveness of the switching retractor.