A vehicle seat has a carriage that moves linearly with respect to a base, and a locking apparatus for preventing unwanted movement of the carriage in the event of an emergency. The locking apparatus has first and second toothed components which inter-engage such that, during movement of the carriage with respect to the base, one of the first and second toothed components imparts movement to the other. A locking gear is engaged with the teeth of the first component for rotation thereby, and is movable into a locking state where it also engages with the teeth of the second component to prevent relative movement between the first and second components. The locking gear moves into the locking state in response to a decelerating force above a threshold level.