A suppressor, also known by the slang term silencer, is a device fixed on the end of a gun's barrel to reduce the weapon's perceptibility. In real life, suppressed weapons are generally still semi-loud, but they also bring advantages such as greatly reduced muzzle flash. Suppressors reduce the sound of gunfire by allowing the rapidly expanding gases from the firing of the bullet to be temporarily diverted or trapped in a series of hollow chambers, known as expansion chambers. The trapped gas expands and cools, and its pressure and velocity decrease as it exits the chambers. Suppressors can fire supersonic ammunition, but this wears out the suppressor very quickly, and is not as quiet as using subsonic ammunition.

In Call of Duty 4: Modern Warfare, suppressors can be used on pistols, assault rifles, or submachine guns. When a player fires a weapon without a suppressor, they will temporarily appear as a red dot on the mini map to enemy players. Firing a suppressed weapon will not cause the player to appear on the mini map in this fashion. The suppressor also reduces shot loudness, muzzle flash, recoil and effective bullet range. Note that a suppressed weapon grants no amnesty from the UAV Recon.

The "invisibility" afforded by the mini-map is invaluable for flanking or ambushing. Even when enemies are alerted to your presence, they must either call a UAV or make a visual in order to locate you. Along with the reduced shot loudness, this makes it much more difficult to locate, and furthermore track, your movements.

The major disadvantage of the suppressor is the reduction in damage over range. Damage over range is reduced to about 70% of its original value for SMGs and pistols, and to less than 50% for assault rifles. It should be noted that at a 25m (or 1000 inch) range and beyond, bullets from a suppressed assault rifle will be dealing their minimum damage, while an unsuppressed assault rifle will still be dealing maximum bullet damage. This emphasizes the use of suppressors as a close to mid range attachment.

Despite the range penalty, powerful and loud weapons such as the AK-47 or the M14 can become somewhat more manageable with a suppressor in certain situations. Such weapons are often plagued with being a combat magnet from the range at which they can be heard firing. With a suppressor, they become particularly devastating at mid range due to the stealth and sheer power.

As the only thing which can reveal a player on the radar while using suppressed weapons is a UAV, the UAV Jammer Perk is an obvious choice for those wishing to take the pure stealth option. A suppressor + UAV Jammer class can easily sow chaos in the rear lines of the enemy ranks. Attaching a suppressor without the UAV Jammer is more risky than choosing a UAV Jammer without a suppressor, as if an enemy player acquires UAV Recon, the player using the suppressor will suddenly be revealed, taking the stealth effect provided by the suppressor away. Therefore, on larger matches, it's preferable to either take both or just the UAV Jammer, as a well-timed ambush can kill many enemies in a short space of time, negating the need for a suppressor as the impending threat of the enemies is removed. As an alternative, a suppressed pistol can be used, acquiring kills without alerting the enemy team of the user's location.

Flanking the enemy may also be an effective technique, achieved by use of Extreme Conditioning. Dead Silence may also be an effective choice, particularly in Search and Destroy, where players often tend to listen carefully for enemy footsteps.

The suppressor attachment is unlocked at 75 kills (Marksman II) for SMGs and assault rifles. The attachment is automatically unlocked for pistols when the pistol itself is unlocked, excluding the Desert Eagle, which receives no attachments.

In singleplayer, it is attached to the USP .45 in All Ghillied Up, One Shot, One Kill, Ultimatum, All In, No Fighting In The War Room and Mile High Club, the MP5 in Crew Expendable, Ultimatum and Mile High Club, the M4A1 SOPMOD in a majority of MacTavish's missions, the M21 in Blackout and All Ghillied Up, and the P90 in All Ghillied Up.

 Working in the same fashion as their Call of Duty 4: Modern Warfare counterparts, the Gewehr 43, and all SMGs except the PPSh-41 can have suppressor attachments to them. Oddly, the Gewehr 43 with the suppressor attached will have the same reload animation for mid-magazine reloading as empty magazine reloading. The reload at partial magazine is hastened so that it takes the same amount of time as a normal mid-mag reload, but if the entire magazine is spent it will reload as slow as it normally would. Enemies will have difficultly finding your exact position if you catch him off guard. Missed shots are also less detrimental with the suppressor, as the enemy will have more difficulty telling where the shots came from, however they will still hear the crack of the bullets flying past them and see the tracer shots. The Flash Hider functions similarly to the Suppressor but is available on the rifles instead, and does not effect the firing sound of the weapon.

Suppressors return in Call of Duty: Modern Warfare 2 as an attachment for submachine guns, pistols, assault rifles, shotguns, sniper rifles, light machine guns, and machine pistols. Launchers, Riot Shields, higher caliber pistols, and akimbo-capable shotguns are the only weapons that cannot accept suppressors. Submachine guns, pistols, and machine pistols suffer the least from equipping a suppressor, as there is only a slight reduction in range with no reduction in base damage. Assault rifles suffer a considerable range reduction, but do not suffer a reduction in base damage. Suppressors reduce Sniper Rifle base damage values from 70 to 50. Without Stopping Power, it will always require (at least) two shots to kill an enemy with a suppressed sniper rifle. Suppressors also reduce base damage values by 10 points on Light Machine Guns. Shotguns suffer an extreme reduction in range when using suppressors, and are considered unusable by most players. Also shotgun suppressors only dampen the sound by 6 decibels or so, a lot less compared to the 50-60 decibels on other weapons. When combined with the perks Cold-Blooded and Ninja, the suppressor makes a player completely invisible to all forms of detection other than being seen or making noise by doing things like falling, switching weapons, defusing a bomb, or shooting, although shooting is obviously much less noticeable when using a suppressor. Strangely all the weapons seem to use the same silencer model. Silencers are unlocked via Marksman challenges.

The suppressor is worth 2000 in Create-A-Class. As in Modern Warfare 2, the Suppressor affects the range of weapons with this attachment rather than the damage, except for the SPAS-12, which has no downsides to having a Suppressor attached as its range is not reduced. The sounds made while firing are the same for most suppressed guns. However the Commando, Galil, AK-47, and M16 do have a unique firing sound when suppressed.