Abstract: A safety device including a locking member which is inserted and locked within the barrel and firing chamber of a firearm to prevent firing of the same is provided. The locking member preferably includes a rod having a leading or first end which is at least partially insertable within the firing chamber of the weapon, and an outer sleeve including a trailing or second end which is expandable in a first direction to produce a tight frictional engagement between the sleeve and the inner wall of the barrel in order to secure the locking member within the firearm. The rod is at least partially insertable within a cavity in a first end of the sleeve such that the overall length of the locking member is adjustable to fit different weapons, for example a revolver and an automatic pistol.