Vault-Tec security enforces the overseer's initiatives and mandates. They are the only residents with authorization for carrying firearms, besides the overseer. They carry out security patrols on eight-hour shifts and are in charge of monitoring for signs of intrusion in the vault, checking for atmospheric leaks (contaminated air getting in), settling disputes between the residents and enforcing rules set down by the overseer and Vault-Tec.
↑Vault 111 security terminal; "Security Personnel: Security patrols are to be carried out on a constant eight-hour rotation. Security priorities include: monitoring for signs of intrusion, checking for atmosphere leaks, settling disputes among personnel, enforcement of regulations set forth by the Overseer, enforcement of regulations set forth by Vault-Tec."