TRW's pretensioner technologies are another element used to help manage occupant energy in a crash. Most pretensioners use a small pyrotechnic charge to help quickly remove excess slack from the seatbelt system and restrain the occupant. Pretensioners can be integrated into the buckle or retractor and take up seatbelt slack using the retractor mechanism or by pulling the seat belt buckle downwards toward the vehicle floor. Once the pretensioner has fired, additional occupant safety system components such as TRW's seat belt retractors and airbag systems will work together to help further manage the energy of the occupant. Pyrotechnic pretensioners, like airbags, need to be replaced once they have been activated.