the invention relates to a belayer / descender safety device , cooperating with a rope , comprising means to hold said rope and rotationally fixed to a chassis on which enclosure means for said rope are mounted with pivoting and cooperating with said holding means . the enclosure means and the chassis comprise a housing in opposition in the locking position which cooperates with a hook means , in particular , a spring hook , wherein said holding means has the form of a pulley housing means for regulation of the speed of rotation thereof .