Belt retractor for a vehicular seat belt system

A belt retractor for a vehicular seat belt system, comprising a belt reel taking up a seat belt, a belt tensioning mechanism capable of biasing said belt reel in a winding direction of said seat-belt, and a sensor capable of triggering said belt tensioning mechanism and provided with a safety device translatable by installation of said belt retractor in a vehicle from a secured condition in which said sensor is blocked, into a released condition in which said sensor is ready to trigger, said safety device including a sensor blocking element which is movable between a blocking position in which said sensor is blocked, and a release position in which said sensor is ready to trigger, and including a transport locking element and a sensing element, said sensing element sensing a diameter of a coil of said seat belt on said belt reel and allowing a movement of said sensor blocking element into said release position only when said diameter is below a predetermined value, said transport locking element being movable between a locked position and a release position, a spring being provided which biases said transport locking element into said release position, and a spring being provided which biases said sensor blocking element into said release position, said transport locking element comprising a retaining section which in said locked position engages an arresting section of said sensor blocking element and maintains said sensor blocking element in said blocking position.