Abstract: A security device for preventing the unauthorized opening of swinging doors. The device has two members, each of which includes two parallel tubes and a rectangular metal plate or web. Each pair of tubes is welded to the respective opposite side edges of its metal plate, and the device is adapted to slide along the floor beneath a door when the door is opened with the tubes of each pair upon opposite sides of the door. The tubes of one member are smaller than those of the other, and the pair of smaller tubes extend beyond their plate toward the other member, and are inserted into the respective larger tubes to a nested position. The overall length of the device is then such that the door can be closed. The members are then moved relative to each other from the nested position, i.e., longitudinally of the pipes so as to span the width of the door. Each pair of pipes has extensions beyond the plate which are then positioned upon opposite sides of the door frames.