Abstract: A locking device for security sealing purposes and of the kind comprising an enclosure element intended to be permanently fixed to an article which is to be locked and a disposable element which is engageable into the enclosure element to close the device and disengageable from the enclosure element by rupture to open the device. The device is characterized in that the disposable element has a plug part which is resiliently deformable so as to be slidably insertable, but not retractable, through an entrance to the enclosure element and which is connected to a head part which projects outwardly of the enclosure element so as to be manually manipulable to detach it from the plug part and thereby open the device.