Cold-Blooded's primary ability is used for the avoidance of killstreak rewards - it allows the user to be invisible to all forms of air support. The vision for Chopper Gunners, AC-130s and Predator Missiles show players with the Perk active, but does not highlight them with a red outline square. Cold-Blooded users can also be killed by collateral damage from other killstreaks, for instance standing between a user of a different tier 2 Perk while a Sentry Gun is firing upon them.
Instead of appearing as bright white silhouettes through a Thermal Scope, Cold-Blooded players will appear as shades of gray similar to the environment, either friends or foes. 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 resolved). 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 silhouettes on the map, it is easy for them to pass right over a Cold-Blooded user.
The Pro version prevents the red name and cross-hairs from appearing on an enemy's screen when they are targeting the user. It is unlocked by destroying 40 enemy killstreak rewards while using this perk. The perk is essential for the "ghosting" tactic, and the Pro version can assist in doing so.
Experienced players use the Pro version in order to play dead, often for "Ninja Defusing", or just to fool enemies who may have hurt them. By going prone, and repeatedly pressing the weapon swap or "cooking" a Stun, Flash, Smoke or Semtex grenade, it will appear as if the player is dead to others.
Call of Duty: Black Ops II
"Resistant to targeting systems including: Dual Band, Target Finder, Sensor Grenade, MMS, and player controlled aircraft. No name or red crosshair when targeted."
"Immune to thermal, target enhancer, threat grenades and enemy call outs. No name displayed or reticle color change when enemies aim at you."
— In-game description.
Cold Blooded Returns in Call of Duty: Advanced Warfare as a tier 2 perk. It renders the player immune to thermal, target enhancer, threat grenades, and enemy callouts. No red name or reticle color changes when targeted.
Call of Duty: Modern Warfare 2
The perk picture shows a lizard surrounded by snowflakes, referencing that lizards are often called cold-blooded creatures.
When killed by a controllable killstreak (Predator Missile, AC-130, Chopper Gunner) the killcam will depict players being killed incorrectly, as it shows a red square around the player's body, even though they would not appear with the square on their monitor normally.
Team members using the Cold-Blooded Perk will not appear white on a friendly thermal scope.
If the player shoots down two Harriers with one Stinger missile and is still going for Cold-Blooded Pro, the two Harrier kills will only count as one.
Conversely, if the player shoots at a helicopter of any kind while it is in the process of crashing with Cold-Blooded equipped, each bullet that hits it will count as another vehicle kill towards the perk's progression (though not towards the player's regular points or experience, except via bonuses from Cold-Blooded's challenges).