The game also features many significant changes and improvements to the series' basic gameplay. Chaos Theory is also the first game in the Splinter Cell series to use ragdoll physics.
Chaos Theory features refined stealth mechanics. In addition to the standard light bar, the game also features an aural monitor that measures the noise that Sam makes, along with the ambient noise of the environment. It is important for Sam to make less noise than his surroundings; otherwise, the enemy guards will hear him.
The AI detection has been altered as well. In former titles, after Sam left an area, the game would do a sweep of the previous area for all unconscious or dead bodies in a well-lit spot. If any were found, an alarm would be triggered. In Chaos Theory, the bodies have to be discovered by a patrolling guard or security camera to trigger an alarm. This enables players to leave bodies laying out in the open, and, as long as the player has eliminated all NPCs and disabled all cameras, no alarms will be triggered.
Being spotted by enemies will still trigger alarms, and alarms will still cause enemies to become more alert and combat-ready (such as causing them to wear ballistic vests and helmets). However, triggering too many alarms will no longer cause the game to end automatically. Even killing civilians or friendly soldiers may not cause Fisher to fail the mission, although doing so will at least cause Fisher to be severely chastised by his superior, and cost him significantly in his mission score as well as cancelling some mission objectives, such as tapping phone lines and locating covert listening devices.
Chaos Theory adds a combat knife to Sam's close-quarters combat abilities. Sam can use the knife in multiple ways, such as threatening an enemy during an interrogation, killing an enemy in close-quarters combat, or piercing gas tanks on generators to aid in his stealth operations. Also, it no longer matters what direction Sam attacks from when using melee attacks, nor does it matter if enemies are aware of his presence, as opposed to earlier entries in the series where he had to attack from behind or on the side, and the enemy could not be alerted to him in order to take them down in one hit. Sam also has the option of using lethal or non-lethal force when ending an interrogation, and with his close-range attacks. As an expansion on Sam's ability to shoot while hanging upside down (introduced in Pandora Tomorrow), he can now choke down or break the neck of enemies below him. He can also pull people over railings while hanging off a ledge and throw bodies off of cliffs or over railings, even onto other guards. However, the ability to shoot around corners has been removed, but this is balanced by being able to switch the side of Sam's body the gun is on while in a firing position.
Fisher can choose from one of three different equipment "kits." There is Redding's recommended kit, an assault kit and a stealth kit. Redding's Recommendation gives Sam an even balance between ammunition and non-lethal weaponry. Assault provides more ammunition at the expense of non-lethal weapons while the Stealth kit contains more non-lethal weaponry at the expense of brute force, lethal weaponry, and spare magazines. On missions where an objective is to cause no fatalities, the player is unable to choose the Assault option.
The 5-7 SC Pistol returns, though the laser pointer featured in Pandora Tomorrow is replaced with a new feature: the OCP (Optically Channeled Potentiator). When fired at certain electronics, the OCP can disable them for a limited time. Fisher can disable lights, security cameras, and more. If the device cannot be disabled, it will temporarily malfunction instead, such as causing the blue screen of death when attacking computer towers. When Fisher successfully disables the electronic device he aimed at, a green light appears on the pistol; if he misses, a red light appears. In both cases, Fisher must wait for the OCP to recharge and become ready for use again.
The SC-20K returns with a multitude of new attachments, such as a foregrip that reduces recoil and increases accuracy, a launcher that fires non-lethal weaponry, an under-barrel shotgun attachment for close quarters firing, and a prototype 20mm sniper attachment for long-range combat. The SC-20K now uses a reflex sight that zooms to 1.5x magnification, while the sniper scope allows from 1.5x to 3.5x magnification.
A large variety of non-lethal weaponry can be fired from the SC-20K launcher, such as the Sticky Camera, the Sticky Shocker, the Airfoil Round, and Gas Grenade. The Sticky Camera will reveal an image of the area in which it was shot. It can also make a clicking sound which will attract enemies, and also emit a CS gas that will render unconscious any enemies in the immediate area. In contrast to former titles, Sam can now use multiple cameras at the same time. He can switch back to any Sticky Camera that has not been destroyed by using the CS gas attack or due to enemy fire. The Sticky Shocker will shock and incapacitate its target when fired. If shot into a body of water, the shocker will incapacitate all targets in the water. The Airfoil Round is a hollow metal ring that will knock out the target. It is still possible for an unconscious enemy to die if shot, dropped from a considerable height or dropped into water, no matter how shallow.
Fisher also has multiple types of grenades. There is a gas grenade, which emits a cloud of CS gas that knocks enemies unconscious, a smoke grenade, which provides Fisher with a cloud of smoke to hide in, the flashbang, which will temporarily blind and deafen any enemy near it, and the fragmentation grenade, which will kill any enemy within its blast radius, and send objects flying in all directions.
