Abstract: An improved firearm safety device for installation on a firearm having a hammer and a barrel. The safety device includes a first section having one end extending around the hammer of the firearm, and an opposite end having an arm provided with serrations formed along a portion thereof. The safety device further includes a second section having a releasable lock and a plug. The lock includes a bore formed therethrough for receiving the portion of the arm having serrations and is operative to lock the second section to the first section, and the plug extends into the barrel of the firearm such that, when the first section is locked to the second section, the one end maintains the hammer in an uncocked, forward position and the plug is retained within the barrel.