Abstract: A lockable safety device that may be installed on handguns, rifles or other firearms having a clip or magazine and an exposed breech area. The safety device comprises an elongated body with a transverse member at one end, and a series of spaced openings along the length of the body, ending before the second end. The openings receive the shank of a padlock. With the slide of the gun retracted to open the ejection port, the safety device is installed by inserting the second end of the body into the ejection port and continually advancing the body through the magazine well until the transverse member engages the upper surface of the slide.