Concussion grenades are very similar to stun grenades. They are designed to deliver concussive trauma to the enemy, disorienting them. It takes 0.3 seconds to prepare and will detonate on contact with the ground or an object after one second. Its effect reaches out to 42.6 feet (12.8m), and the thrower will receive a hit marker if the enemy is within this range.
It should be noted that it is possible for the player to stun him or herself, although this produces no hit marker. It is also possible to stun a friendly in hardcore game types, which does produce a hit marker.
Concussion grenades detonate after a certain time period AND when they impact an object or the ground, whereas flashbangs detonate only after a certain time period. This means flashbangs may detonate while still airborne, when concussion grenades will always 'wait' until they hit something. This is an advantage for using the concussion grenade, because if the grenade is being thrown over a long distance, a flashbang may detonate in mid-air before reaching the target, but a concussion will not.
Using concussion grenades has severe disadvantages when the enemy is already aiming in the player's direction because their visibility will barely be altered, and they can still fire and kill the player without moving their reticle that much. Therefore, moving quickly after using a concussion grenade is more important than with a flashbang.
One of the disadvantages of the concussion grenade is that the actual blinding radius is lower than the flashbang's radius. However this isn't needed as much because it slows movement. This allows for the killing of unsuspecting targets more effectively.
If a player is hit by a flashbang, and are aware of their surroundings, they may be able to blindly run for cover, and wait for the flash to wear off. However if the player is hit by a concussion grenade, they are slowed down a great deal, so are often not able to get to cover. Therefore, a concussion grenade is more useful against a moving target who isn't aware of the thrower's location, and a flashbang more useful against players who may be aware of the thrower's location and are looking in that direction.
The Concussion Grenade appears once again in Call of Duty: Modern Warfare 3. The Concussion Grenade has two notable changes. One being the longer pin pull animation and the second being the larger radius affected by the blast. It does the same basic thing as its Black Ops counterpart, with the exception of a slightly whiter screen when being affected by one. It is unlocked at level 4 in Multiplayer. Stunning an enemy counts as "tagging" an enemy while using Recon.
It looks like the flashbang from previous games, with a white wrap instead of a red one.
The Concussion Grenade returns in Call of Duty: Black Ops II. It is essentially unchanged from previous Call of Duty games. In multiplayer, each concussion grenade costs one Pick Ten point, up to a maximum of two grenades. Concussion grenades can be rendered almost totally ineffective by the Tactical Mask perk.