Seatbelt pretensioners are safety devices in vehicles designed to enhance the effectiveness of seatbelts during a collision. When a crash is detected, these devices quickly tighten the seatbelt, pulling the occupant closer to the seat. This helps to reduce the risk of injury by minimizing the movement of the body during impact. The pretensioners work in conjunction with other safety features, such as airbags, to provide better protection. By ensuring that the seatbelt fits snugly against the occupant, pretensioners help to keep individuals in the safest position possible, thereby improving overall safety in the event of an accident.