A Ferengi gas canister was a device discovered by Enterprise in 2151 on the surface of an unexplored moon. Unknown at the time, the device was planted by the Ferengi to be taken aboard unsuspecting starships. Once aboard and triggered, the device, believed to be an ancient artifact, released an anesthesia gas throughout the ship when T'Pol opened it, putting the entire crew to sleep.
This device, used by Ferengi merchant Ulis, was utilized to incapacitate the Enterprise crew, allowing the Ferengi to board the ship and raid it for valuables. Such a device had been previously used by Ulis and his crew to incapacitate and raid a Gavarian ship. (ENT: "Acquisition")