From Lexicanum

A Null Rod is a type of Power weapon used by members of the Ordo Malleus's Daemonhunters. These obsidian rods constantly crackle with anti-psychic power which nullifies the powers of the Warp. However, this device also prevents the wielders themselves from making use of any psyker power.¹

Sources

• ¹:Codex: Daemonhunters (3rd Edition), pg 18

See also

• Daemonhunters Armoury