Cold-Blooded

From the Call of Duty Wiki

Cold-blooded is a Tier 2 perk unlocked at level 25 appearing on Call of Duty: Modern Warfare 2 that makes players undetectable to all killstreak rewards and thermal imaging. Players using Cold-Blooded will be invisible to the UAVs, Sentry Guns, Harriers and computer controlled Helicopters and simply will not be targeted. With Predator Missile Strikes, 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. Viewed through thermal scopes instead of appearing bright white, Cold-Blooded players will appear as shades of gray similar to the environment, However this may cause the player a disadvantage on snow maps, as the gray has more contrast with the environment, whereas the white-hot non-cold blooded players are 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). Just as in the original Modern Warfare in which silencers and the UAV Jammer perk were mixed.  

[edit] 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 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, using the Cold-Blooded perk will keep them from being exposed until they kill an enemy or are killed themself.

[edit] 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. Once the Pave Low has been destroyed shoot at it as it is falling out of the sky. For every bullet that hits the Pave Low, it counts as 1 kill. It is quite possible to get 30-60 'kills' towards the challenge this way for each Pave Low. The Pavelow has to be destroyed by bullets, not a launcher such as the Stinger as the Pavelow is completely blown up by these. The wisest weapon to use for this would be an LMG like the L86 LSW as it has a high rate of fire and large magazine. A Silencer may want to be attached to hide your constant spraying from the enemy radar.

Perks of Call of Duty: Modern Warfare 2
Tier 1 Perks	Marathon · Sleight of Hand · Scavenger · Bling · One Man Army
Tier 2 Perks	Stopping Power · Lightweight · Hardline · Cold-Blooded · Danger Close
Tier 3 Perks	Commando · Ninja · SitRep · Steady Aim · Scrambler · Last Stand
Kill Streak Perks	3: UAV Recon · 4: Care Package · 4: Counter-UAV · 5: Sentry Gun · 5: Predator Missile · 6: Precision Airstrike · 7: Harrier Strike · 7: Attack Helicopter · 8: Emergency Airdrop · 9: Pave Low · 9: Stealth Bomber · 11: AC-130 · 11: Chopper Gunner · 15: EMP · 25: Tactical Nuke
Death Streak Perks	Copycat · Painkiller · Martyrdom · Final Stand