Cold-Blooded

Cold-Blooded is a Tier 2 perk in Call of Duty: Modern Warfare 2 ' s multiplayer. It is unlocked at level 25. This perk removes the player's thermal silhouette when viewed by thermal optics, and makes players undetectable to all killstreak rewards. Players using Cold-Blooded will be invisible to the UAVs, Sentry Guns, Harriers and computer controlled Helicopters and simply will not be targeted (though players can still be killed by collateral damage from these sources). With Predator Missile, AC-130 and Chopper Gunners, players using this perk will still appear on the screen but they will not be highlighted by a red square. Thus, the best strategy during one of these kill streak attacks is to simply stop moving as the black and white resolution for such attacks is poor and moving objects are much easier to see.

Instead of appearing as bright white silhouettes through a Thermal Scope, Cold-Blooded players will appear as shades of gray similar to the environment. This may actually cause the player to be at a disadvantage on snow maps, as the gray has more contrast with the environment, whereas the white-hot silhouette of non-cold blooded players is much harder to spot against the white snow (of course, for this reason, most players choose not to use Thermal Scopes on winter maps, so the issue is often moot). As they are not truly invisible, moving Cold-Blooded players are much easier to spot through thermal scopes than stationary ones. As most Thermal Scope users are more accustomed to bright white blots on the map, it is easy to pass right over a Cold-Blood user.

The Pro version prevents the red name and crosshairs from appearing on an enemy's screen when they are looking at the user. It is unlocked by destroying forty enemy killstreak rewards (of any kind, even UAVs) while using this perk. If a silencer is added this is very helpful to sniper classes (though damage is reduced).

Tips

 * One of the most efficient ways to utilize this perk is either in Search and Destroy, or with an Anti-Support class. As an Anti-Support class, unless a friendly is next to you, or an AC-130/Chopper Gunner is taking pot-shots, they will not attack you, letting you both unload your magazine and rockets without the threat of immediate annihilation from the vehicle above you. In Search and Destroy, when coupled with a suppressor and Ninja, you become almost invisible to all but direct sight. Unless the enemy has SitRep Pro you can sneak up to anyone and give them a quick tap-out with your trusty knife.
 * With this perk it is not safe to stand next to someone without it during an enemy killstreak. They will be targeted and you may be killed with them when they are hit. However, in friendly fire games, you will be safer, as the average player will not attack players without red boxes since they will assume that you are friendly. Because of this, players trying to shoot down enemy aircraft with Cold Blooded should stand away from team-mates.
 * Players using a "Knife Monkey" strategy may want to try this perk, as the Knife Monkey tactic is to flank and or sneak up on an enemy. They can then use their tactical knife for a quick and instant kill. heavily relying on stealth the knife Monkey is at their weakest when an enemy U.A.V exposes them on the mini-map, although using the Cold-Blooded perk will keep them from being exposed until they kill an enemy or are killed themselves.
 * Cold-Blooded is useful for Ninja Defusing as well. Since Cold-Blooded hides you from any form of detection besides direct enemy eyes, even if the enemy has called in a U.A.V Recon, you will not show up on radar. Without Cold-Blooded, the bomb planter could spot you on the U.A.V while he is planting the bomb. If he were to catch this, he'd turn around and you would most likely be shot down. In addition to being hidden from radar, the Pro version of Cold-Blooded hides your name and red cross-hair if the enemy is looking at you, making it easy to hide in shadows around the map.
 * If you are looking to get a Tactical Nuke, it is suggested that you use Cold-Blooded.

Trivia

 * The perk picture shows a lizard (a "cold-blooded" reptile) surrounded by snowflakes.
 * In reality, "Cold-Blooded" refers to an organism that cannot produce its own heat, referring to the fact that most of the weapons this perk blocks use body heat as a means of targeting.
 * There are three ways of obtaining the Pro version of this perk: shoot down enemy air support with a launcher, steal enemy care packages, or destroy enemy sentry guns.
 * There is a glitch which allows a player with this perk to collect points towards the challenges very easily. This requires the enemy to call in a Pave Low or Attack Helicopter. Once it has been destroyed shoot at it as it is falling out of the sky. For every bullet that hits it, it counts as 1 kill. It is quite possible to get 30-60 'kills' with an assault rifle or sub machine gun, or even well over 100+ with a rapid firing light machine gun such as the M240, or MG4, towards the cold-blooded pro challenge this way for each Heli. The helicopter has to be destroyed by bullets or by calling in an EMP, not a launcher such as the Stinger as it is completely blown up by these. However, the Harrier will not blow it up, so you can also destroy it with Harrier. A Silencer may want to be attached to hide your constant spraying from the enemy. Using an AT4 or RPG-7 to damage the Pave Low first can help reduce the number of bullets required to destroy the helicopter, since they do not destroy the helicopter in one shot.

When one of your killstreaks comes to the map and you have Cold-Blooded equipped, the enemy cannot shoot down your killstreak.