The most common occupant protection system in use is the three-point automatic seat belt which secures you in your seat in the event of a collision and slows you down at the same rate as the passenger cell in which you are sitting. The automatic inertia reel seat belt is easier to fasten and more comfortable. The belt stopper is a mechanical locking system which traps the belt above the reel, stopping the film reel effect. Belt pre tensioners compensate for belt slack by tightening the belt on impact, pulling it tighter to your body. The belt force limiter, working with the pre tensioners and airbags, reduces the risk of injury to your upper body.