Abstract: A theft preventing device for an article having a substantially cylindrical end with a substantially ring-shaped bulge, e.g. a bottle or container. The device comprises a releasable body having a clamping means gripping the cylindrical end when in the closed position, and a locking means for preventing the clamping means from being opened unless a special tool is used. The body comprises of a substantially tubular element with a larger diameter than the ring-shaped bulge, and comprises a member that is movable relative to the tubular element between a closed position in which it defines a cross-section smaller than that of the ring-shaped bulge, and a released position in which it defines a cross-section greater than that of the ring-shaped bulge.