These units are typically put in in buildings and various constructions to warn occupants on the presence of a fireplace and to facilitate evacuation. Provision of telephones suitable with Listening to aids, marked With all the conventional ear and ‘T’ symbol and Geared up with inductive couplers and volume controls. https://www.firesense.co.uk/type/conventional-fire-system/conventional-sounders-vids-vads/