Elevator

The Elevator appears briefly in Call of Duty 4: Modern Warfare, Call of Duty: Modern Warfare 2, and Call of Duty: Modern Warfare: Mobilized, and appears as a regularly usable utility in Call of Duty: Black Ops on the multiplayer map, Hotel and the Zombies map, "Five".

Call of Duty 4: Modern Warfare
In Ultimatum, Price, Griggs and Soap ride an elevator to get to the vehicle depot.

Modern Warfare 2
Elevators are seen in the level "No Russian". Two guards ride up on one, attempting to stop the terrorist attack. The elevator is then blown up by a grenade. If the player kills the guards before they enter the elevator, the player can click the elevator button and use it instead of the escalator, but if Makarov blows it up, you can use the one right next to it. taking the elevator is actually longer, because you have to walk around a big wall to reach the exit.

Modern Warfare: Mobilized
An elevator is used by Sgt. Baker and Captain Weston.

Hotel
Hotel is the first multiplayer map to feature elevators. They take players to the upper or lower levels of the resort, often leading to the inside of the hotel or to useful sniping positions.

"Five"
The first elevator players are able to use is on the same level as the players spawn, and leads to the second level of the war room. This elevator is very small, with barely enough room for all 4 players. It is elegant, featuring polished wood walls and a marble ceiling with several plaques that serve only for aesthetics and humor. Because of its small nature, there's only 1 entrance. The other elevator is located at the bottom of the war room.

Unlike the first, this elevator is much bigger, all 4 players and dozens of zombies can easily fit in. It resembles a very large cargo elevator. Also unlike the first elevator, this one has 2 entrances. The first being the main door, and the second being a barrier where zombies can break in. The entrances face different directions at different levels.

On both elevators, players can call the elevator if it is not on the same floor as them. Also, players can use this method for free rides if the players are on separate floors which allows players to save money and work together. Camping in elevators is an extremely popular method, as players can hold off in the elevator until things start to get hectic, where a player can take the elevator up or down as short break to allow reloading, reviving of any downed players, or to simply let the suspense of a nerve-wracking close call die down.

Elevators are overall more reliable than teleporters in Five, as they can be camped in, used for short relief, and are more predictable than the teleporters, which take time to memorize the locations they're connected to. But if used foolishly, the elevators can also lock the players in an inescapable corner. Players can also misuse the elevator by using it when other players aren't in it, thus leaving them behind to be killed. Elevators are a lot like the zipline for these reasons, as both can be camped on and used for quick escapes.

The elevator cannot be used during the thief round. Players will get the "Access Denied: Security Protocol 115" message when attempting to use it.

Trivia

 * In "No Russian", If you kill one of the FSB going to the elevator, but leave the others, the game stops, because Makarov is scripted to kill the guards. The terrorist squad will stop and the FSB will also stop in the elevator. If you go all the way down and ride the elevator, the FSB will go through the floor of the elevator. The only way to continue the mission is to kill the remaining FSB.
 * If a player or a horde of zombies stand in the doorway of the elevator, it cannot be used. Displaying the message "Elevators doors blocked" upon use.
 * Also, in the service elevator, if a player is guarding the window, it will say " Elevator doors blocked."
 * If there is a downed player in the elevator on "Five" any other players who try to use the elevator will fail and the player's character will comment that "They cannot afford the ride up/down". (Confirmed on PS3)
 * Power-ups will float up or down when the elevator is used. This sometimes applies to dead zombies too. This can be rather handy since the gas from any gas zombies will also float away.
 * There have been some cases of extreme lag where the player managed to clip through the Elevator and go into the shaft.
 * If a player jumps on a teammate when going down, they can glitch out of the elevator, making them invincible but also incapable of killing any zombies.
 * For some reason all sides of the elevator shaft are properly textured, including the ceiling and floor, even though it is not possible to see them without glitching or cheating.
 * On consoles, if there is a zombie in the elevator when the elevator is moving, the player's aim will forcefully point above or below the zombie. This is a bug with the aim assist.
 * The elevator doors cause damage, and destroy equipment on Hotel.