An inertia reel, also known as a seat belt retractor, is a type of device commonly used in automobiles to secure passengers in their seats. However, there are several synonyms for the word inertia reel, including retraction harness, seatbelt harness, and automatic seat belt. Each of these terms describes a similar type of mechanism that keeps passengers safely secured in their seats during a collision or sudden stop. Other synonyms for the term inertia reel may include automatic seat belt tensioner, automatic locking retractor, and self-locking seat belt. Regardless of the name, each of these devices plays a critical role in passenger safety while traveling in a vehicle.