The Simplex 2901 series bells are modular in design and provide a loud penetrating sound output that is easily heard over most ambient noise levels. The 2901 series bells are designed for installation on a standard four inch square electrical box or two inch (gangable or non-gangable) switch box. Bell guards, which cover the entire unit, are also available for any bell size. The 826 yard hood is designed for outdoor use to mount a bell mechanism with bell gong on a weatherproof box. It is designed to allow a maximum amount of signal level to radiate from the hood outwards, yet protect the audible device from the elements. Weatherproof applications require a weatherproof back box, Model BBX-4.
More Info, please download datasheet bellow: