Horns, Sirens & Whistles

A siren is a loud acoustic alarm device that produces a loud wailing noise to warn of an obstruction or to alert sailors to emergencies.

A foghorn is a fog signal that uses sound to warn vehicles of navigational hazards, or boats of the presence of other vessels, in foggy conditions. The term is most often used in relation to marine transport. When visual navigation aids such as lighthouses are obscured, foghorns provide an audible warning of rock outcrops, shoals, headlands, or other dangers to shipping.

A whistle is another sound buoy aid to navigation. The whistle is usually placed as a warning of a dangerous area, a sound signal of a ship, used in fog or to indicate intentions when maneuvering near other ships.