A locking box magazine safety device, comprising a magazine body comprising a rigid material shaped to conform to the internal dimensions and features of a box magazine well in a magazine-operated device; a lock cylinder comprising a key-operated lock and an operating rod, the operating rod configured to move when the appropriate key is used in the key-operated lock; and a pivoting arm configured to pivot about an axis, configured to be fixed in place by the movement of the operating rod, and configured to obscure the action of a magazine-operated device when fixed in place.