Brass air whistles were used in the last century primarily at industrial locations and military installations. The use of brass in the manufacture of these whistles gave them clear and vibrant sound , just as a brass section in a orchestra does. The air whistles were usually mounted on the outside of buildings to signal a fire alarm or drill, or some other emergency. The patina of the brass air whistles that have weathered 50 or more years outside will be a beautiful aqua blue and are highly prized for this trait.