These codes are usually only known to a handful of people within the facility so as to prevent unauthorized exits. (Only Vault 87 and Vault 19 had any other entrances.) Most vaults have consoles located on both the inside and outside, either of which requires a security code to open the outer door. For most vaults this is the only means of entering or leaving. It is closed from the inside by a reinforced high-security door and from the outside by a massive, gear-shaped, four-foot thick vault door, which Three Dog claims 'weighs, like, thirteen tons'. The entrance houses the Vault's only connection to the outside world - the airlock (with the exception of Vault 19 and Vault 87). However, many doors within in-game vaults are inaccessible, which allows for the possibility that the vault is far larger than the areas the player can access. None of the explorable vaults in the games have enough space or facilities to actually house 1000 people (or rather 500, as hot-bunking is used at maximum capacity). It should be noted that due to scaling, the size of vaults in games shouldn't be taken at face value.

The vaults of the West Coast differ from those constructed in the vicinity of Washington, DC and the Mojave area.

The vaults are all very similar in their basic functions, but sometimes were constructed according to different designs.

Fallout shelter vault layout ideas