Armor

The standard armor (known as security armor in the manuals) is an item that appears in the Doom games as a bright green military vest, similar to the one worn by the player sprite. When collected, it increases the player's armor percentage to 100. It cannot be collected if the player already has at least 100 percent armor. When an armor is obtained, the game displays a HUD message: picked up the armor.

The armor will absorb one third (1/3) of all damage received, rounded down, until it is fully depleted.

This item is not counted in the items percentage displayed at the end of each level.

Data
In classic Doom, armor is first encountered on these levels:

The IWADs contain the following numbers of armors per skill level:

Other games
In Doom RPG, the armor is called a flak jacket. It increases the player's armor rating by 25 units.