A belt retractor for a safety belt system includes a frame, a belt reel rotatably mounted in the frame, a force limiter, a locking mechanism which couples the belt reel in a restraint case to the frame via the force limiter, and a belt webbing unwinding measuring means which includes a signal transmitter and at least one sensor. The sensor is associated with the signal transmitter and detects a change in a magnetic field. At least upon activation of the locking mechanism the signal transmitter is coupled to the belt reel such that it generates a signal upon rotation of the belt reel.