Seat belt retractor

The device (10) has a belt spool, a retractor locking pawl that blocks belt unwinding in an accident and a tightening device (30,50,60,70,100) for tightening the belt in a hazard situation with a tightening locking pawl (30) that locks the belt in the unwinding direction when locked or releases it. The tightening locking pawl has an associated sensor (100) for monitoring its position outputting a corresponding signal to a controller (60) for the tightener.