A building security assembly includes a vestibule that may be attached to an entrance of an institution and the vestibule has an entrance and an exit. A first door is hingedly coupled to the vestibule to open and close the entrance. A second door is hingedly coupled to the vestibule to open and close the exit. A metal detection array is positioned within the vestibule to detect metal components of a firearm. A security unit is coupled to the vestibule and is in electrical communication with the metal detection array. The security unit locks each of the first and second doors when the metal detection array detects the metal components of the firearm to inhibit the individual from bringing the firearm into the institution.