The Anti-Vampire Device is a weapon the British Men of Letters at some point invented through a combination of technology and magic that releases a gas that is poisonous to vampires and can kill them. It is sometimes shortened to AVD.
Cylindrical in design, the AVD has various Enochian symbols written at the ends of the device. When activated, the AVD emits a smoke, which causes vampires to suffocate and die. While deadly to vampires, the toxin in the AVD leaves humans unharmed.
The AVD is used by Mary Winchester and Arthur Ketch to take out a vampire nest. Mary later attempted to retrieve the device at the British Men of Letters' armory to kill the vampires that were attacking the compound but was stopped by Pierce Montcieff. He knocked her out and stomped the AVD, destroying it. It is revealed that he worked for the Alpha Vampire. The Alpha Vampire later gets killed by Sam Winchester with the Colt and Pierce gets taken into custody by Arthur.