Abstract: A firearm safety device including a stop tab, a locking strap and a lock tab. The stop tab has an inner end adapted to abut against the muzzle of a firearm. The locking strap is attached to the stop tab and is adapted to be insertable into and through the barrel of a firearm. The locking strap has a plurality of transverse teeth located on an outer surface thereof. The lock tab is removably attached to the stop tab and has a lock housing with a transverse aperture extending therethrough that is adapted to receive the locking strap. The lock housing is adapted to allow the teeth of the locking strap to pass through the transverse aperture as the lock tab is being inserted onto the locking strap, but to prevent removal of the lock tab from the locking strap once insertion has started.