Abstract: A safety device for garage doors wherein the door can be pulled down against the opposition of one or more torsion springs acting upon a horizontal shaft has a housing for a gear which is non-rotatably mounted on the shaft and whose peripheral teeth and tooth spaces are adjacent a set of recesses the the housing. A plastic casing which is biased by the torsion springs normally maintains in deformed condition at least one coil spring which reacts against the housing and tends to rotate the casing relative to the gear so that several ramps which are adjacent to discrete pockets of the casing expel from the recesses spherical blocking elements which normally extend partly into the recesses and partly into the adjacent pockets. This results in partial entry of blocking elements into the adjacent tooth spaces to thus hold the shaft against rotation relative to the housing in the event of breakage of the torsion springs.