A safety device for detachably locking the output member of a linear drive, comprising: - a coupling rod which can be coupled to the output member of the linear drive, - a housing through which the coupling rod passes in a linearly displaceable manner, - a blocking unit through which the coupling rod passes in a linearly displaceable manner and which is movable, relative to the housing, between a blocking position which blocks a stroke of the coupling rod and a release position which allows a linear movement of the coupling rod, - a spring means for preloading the blocking unit in the blocking position, - a locking means for locking the blocking unit in the release position, the locking means comprising locking rolling bodies (34a-c) received in the housing and a support sleeve through which the coupling rod passes in a linearly displaceable manner, it being possible to move the support sleeve between a support position, in which the support rolling bodies (34a-c) are held in a locking position radially outwards in locking engagement with the blocking unit, and a release position, in which a retraction of the support rolling bodies (34a-c) radially inwards out of engagement with the blocking unit is made possible, - an electromagnet means which, when energized, holds the support sleeve in the support position against the actuating force of at least one release spring of a release spring means in such a way that, in the event of a power failure, the holding function can be reversed and the support sleeve enters the release position by means of the at least one release spring, as a result of which the blocking unit can be transferred into the blocking position by means of the spring means; characterized in that a stop is formed on the coupling rod and a counter-stop is formed on the blocking means, which stop and counter-stop are arranged in the release position at an axial distance relative to one another that determines the stroke of the coupling rod and, in the blocking position, abut one another so as to bring about the locking of the output member. - a coupling rod which can be coupled to the output member of the linear drive, - a housing through which the coupling rod passes in a linearly displaceable manner, - a blocking unit through which the coupling rod passes in a linearly displaceable manner and which is movable, relative to the housing, between a blocking position which blocks a stroke of the coupling rod and a release position which allows a linear movement of the coupling rod, - a spring means for preloading the blocking unit in the blocking position, - a locking means for locking the blocking unit in the release position, the locking means comprising locking rolling bodies (34a-c) received in the housing and a support sleeve through which the coupling rod passes in a linearly displaceable manner, it being possible to move the support sleeve between a support position, in which the support rolling bodies (34a-c) are held in a locking position radially outwards in locking engagement with the blocking unit, and a release position, in which a retraction of the support rolling bodies (34a-c) radially inwards out of engagement with the blocking unit is made possible, - an electromagnet means which, when energized, holds the support sleeve in the support position against the actuating force of at least one release spring of a release spring means in such a way that, in the event of a power failure, the holding function can be reversed and the support sleeve enters the release position by means of the at least one release spring, as a result of which the blocking unit can be transferred into the blocking position by means of the spring means;