Active camouflage

The Active Camouflage power-up is light-bending energy stored in a small, glass-like pyramid in Halo: Combat Evolved and Halo 2. In Halo 3 it is suspended in a spherical force-field. It is similar to the way a Covenant overshield functions. When the player breaks the active camouflage container (done by simply walking over it), the energy envelops the wearer and bends light around the skin, armor, or shielding, conforming to its user's form and rendering them almost invisible. This effect wears off as the energy dissipates and the user slowly becomes more visible.

Function
The Camouflage covers the entire body, but it does not extend to the entirety of the user's equipment. Human weapons won't give away the user's location, although Covenant weapons, mainly glowing becasue of plasma will be seen. The Energy Sword in Halo 2 is visible even while you are invisble, this problem is fixed in Halo 3. Also, if close enough, the character's outline is seen faintly and looks like a moving silhouette. However, it is hard to see the outline and the "ghost" from a far angle. Even on a scoped weapon, like the Sniper Rifle or Battle Rifle, it can be difficult to see a camouflaged opponent. When any projectiles pass through the shielding (whether by firing a weapon or being shot), it is temporarily deactivated, making the user partly visible.

The technology can be utilized on Human armor systems, such as the MJOLNIR armor, but the UNSC has only developed a rough equivalent, the Camouflage Cloak.

Some Elites have active camouflage generators, as do some SpecOps Grunts. The Arbiter has old armor with an obsolete active camouflage generator that needs to recharge after using the camouflage for too long. In Halo 2, it is noted that the Arbiter's armor, while possessing an in-built active camouflage generator, is not permanent until turned off, unlike the more modern generators used by SpecOps Elites. There is a circle on the player's HUD that shows the amount of time left for both the usage of the active camouflage and the recharging sequence. The Master Chief can gain this ability with the Envy Skull.

When playing as the Arbiter, using any attack will cause the active camouflage to deactivate, and the player must wait for it to recharge before using it again.

Science
Technically, Active Camouflage is not quite invisibility, though it is similar. Rather, is the term that is used to describe a broad range of technologies that a wearer or object with its terrain, mimicing the environment around it perfectly, though in two dimensions. There are a variety of ways to do this, though the UNSC uses photo-reactive panels on its Semi-Powered Armor and Prowler warships for optical camouflage, adapting to account for movement.

Though it has never been elaborated on in detail, it is suspected that Covenant versions of the concept use phased array optics to project a three-dimensional hologram of background scenery around the wearer of the system, a task well within the Covenant's technological level.

Use in Campaign
If the active camouflage is active during campaign, your are completely invisible to the AI enemies unless you fire your weapon which will deactivate the camouflage for a short amount of time. Active camouflage is only usable in campaign when you are playing as the Arbiter in Halo 2, pick up Cloaking in Halo 3, and in four levels in Halo: Combat Evolved: Truth and Reconciliation, Silent Cartographer, 343 Guilty Spark, and Assault on the Control Room. In Halo 3, Active Camouflage is a piece of equipment that can be picked up much like the Bubble Shield or other items. What makes this beneficial is the item can be used when needed, not just when available. The user can hold on to it until it is required in a situation when he's drastically outnumbered. Activating the Cloaking can even the odds or avoid contact all together.

Active Camouflage and Shielding
An odd discrepancy is present in the difference between Halo: Combat Evolved and Halo 2 active camouflage. In Halo: Combat Evolved, Stealth Elites using active camouflage had no shielding whatsoever; furthermore, Elites were the only Covenant to possess it. However, in the last level, an Elite Flood Combat Form was seen with an Active Camouflage, but this was presumably an infected Stealth Elite. In Halo 2 active camouflage was seen in use by both Elites and Grunts, during The Arbiter and part of Regret.

In "A Day At the Beach," an Elite Minor is seen engaging his own active camouflage at the expense of his shields (though when the camouflage seems to be shorted out by the plasma grenade explosion his shields are reactivated).

It can be conjectured from this evidence that perhaps all Elite armor has active camouflage systems installed, but in all but the highest echelons of Elite rankings the power drain deactivates the shield in favor of the camouflage. Only Ultra Elites and Special Operations Elites seem to have enough power in their armor to run both systems at the same time.

Halo 3 Active Camouflauge
The Active Camo is no longer contained inside a pyramid. Instead it appears as a large, glowing sphere with what appears to be containment devices around it in Halo 3 multiplayer. Unlike past Halo games, active camo is not found in campaign. In campaign, Active Camouflage is replaced by the Cloaking equipment, which functions in the same way as active camouflage once used. Melee attacks, shooting, throwing grenades, and using equipment will negate the effect of the power-up.

The quality of camouflage in custom games may be set to two different settings :
 * Poor Camo: The player has camouflage that might fool a Grunt.
 * Good Camo: The player has camouflage that will fool an attentive Elite.

Spartan-III
The Spartan-IIIs use a version of Active Camouflage, using panels to mimic the surrounding environment. This feature was tested by ODSTs, and saw limited use in 2552.

Trivia

 * By changing the graphics card settings on Halo PC, active camouflage users appear as a big, single-color figure and are very visible.
 * When invisible and switching to a depleted energy sword in Halo 2 and Halo 3, the outline of the swords plasma blade will still shimmer even though it is depleted.
 * Active camouflage covers the Energy Sword in Halo 3, unlike in the previous games where it remains fully visible.
 * On 343 Guilty Spark if you go right off of the fallen tree towards a small indention in the hill, you will find an Active Camouflage next to a pipeline.
 * Active camouflage generates heat, which can be taken advantage of by the use of infrared equipment by UNSC forces.
 * The Separatist Phantom in Halo 3 has its own Active Camouflage generators on board for various stealth missions.
 * Even though you will be invisible in multiplayer you can still be tracked by the motion tracker.
 * When you shoot or melee with Active Camo on it will disappear off for a couple of seconds.
 * When using cloaking in Halo 3, it's not suggested that you use a Gravity Hammer because the lights emitted by the hammer will still be visible but an energy sword can be unsheathed without a sound and held without a light giving you away.