From Halopedia, the Halo wiki
This article is about the piece of equipment in Halo 3. For the technology and the in-game items in other games, see active camouflage.
Cloaking appears as a form of equipment in Halo 3. Once activated, it has the same basic function as active camouflage from the first two games: it renders the user nearly invisible. Unlike active camouflage in the previous games, cloaking is a piece of equipment—it can be activated whenever the player chooses to, whereas active camouflage is automatically activated when the player collects it. In addition to being more portable, cloaking is also more effective in Halo 3 than Halo: Combat Evolved's active camouflage -- while in Halo: Combat Evolved, the entire body can be seen faintly, in Halo 3, only a faint shimmer can be noticed. There is a disadvantage to cloaking, however -- it only lasts for ten seconds, after which its effect fades over the course of an additional two seconds.
Like active camouflage, firing a weapon, performing a melee, tossing a grenade or coming under fire slowly begins to disrupt the effects of invisibility and brings the user into sight. Cloaking also does not mask environmental effects or any shadows cast by the user, so it is less effective on maps where footprints can be left or where shadows can easily be seen.
The symbol for the cloaking on the heads-up display resembles the active camouflage power-up from the first two games - a triangle with an eye in the middle. Enemies will not notice you while you are camouflaged as long as you do not do anything to disrupt it, as noted above, or bump into them. If you activate it in plain sight during a battle, enemies will still know your location. It should be noted that Brute Chieftains can occasionally sense your location, turning slowly as you move and attacking if you get within a few feet.
Cloaking can be found on many levels in campaign, but it is not present in multiplayer. Cloaking is first seen in Halo 3's second campaign level, Crow's Nest. Cloaking appears most frequently on the Halo 3 Campaign level Cortana. It can be quite helpful on Heroic, Legendary, and Mythic.
List of appearances