Gas Capsules (sometimes referred to as Gas Pellets) are tools used by Batman. Often stored in the Dark Knight's Utility Belt, they release airborne agents designed to incapacitate or subdue hostiles. The contents of the capsules have often changed, though the most commonly stored are tear gas.
Functionality
Though their design and contents has often changed over the years, the gas capsules' functionality has always remained the same. In most stories, they are small vials or containers holding chemical agents. When they make contact with a solid object or opponent, they release a gas designed to incapacitate or restrain them. Depending on the time period and writer, they contain either choking concoctions, tear gas, or smoke laced with sedative agents. Batman and the Bat-Family have mostly made used of Smoke Capsules, which release clouds of thick gas to disguise their movements.
History
Gas Capsules first made their appearance in Detective Comics #29. In their first appearance, they were vials of chemicals that, when mixed, created choking gas. Batman used them to create diversions to escape or to incapacitate he opponents. The lethality of these mixtures was, at most, debatable, though Batman use them to cause the deaths of several opponents, such as Carl Kruger and one of Hugo Strange's Monster Men.
In Batman #2, an injured Batman made use of a Smoke Capsule to allow him and Robin to escape from Adam Lamb and his Wolf Mob. After a mandate by editor Whitney Ellsworth to stop the character from killing, these capsules began to be more widely used than the choking gas pellets. In subsequent stories, Batman began to use chemicals that would render opponents unconscious.
After tear gas was allowed to be used by police forces in riot control, Batman also began to use the chemical in his arsenal to deal with large groups of enemies or riot control. In The Dark Knight Returns, Batman makes use of chemical agents that induces hallucinations and paranoia against several of Harvey Dent's men.
In Other Media
Live-Action
Burton Films
In the 1989 Batman film, Batman makes use of glass vial smoke capsules to escape several incidents. Promotional material refers to these as "Gas Capsules", though no other chemical agent is shown or used. The capsules are also not used in the sequel Batman Returns. However, the manual for the SNES tie-in game mentions that Batman makes use of green knockout-gas capsules in addition to blue napalm ones.
Dark Knight Trilogy
Smoke or other gas capsules are not used in any entries in the Christopher Nolan Batman film series. However, guide books for Batman Begins reveal that he keeps them on his Utility Belt.
Batman v Superman: Dawn of Justice
A Kryptonite Gas Grenade is used against Superman
Batman is depicted using either military fashion smoke grenades or 40 mm gas grenades, the latter fired from a grenade launcher. After stealing Kryptonite from LexCorp, he fashions three of the latter to release an airborne variant of the substance. Two of them are used to weaken Superman during their fight while the final one is used against Doomdsay.
Animation
Batman: The Animated Series
In several episodes of The Animated Series, Batman makes use of tear gas to incapacitate groups of criminals, usually during raids with the GCPD. However, his smoke capsules are also mentioned to be lined with a sedative which knocks those who breath them in unconscious.