Foghorn

Device using sound to warn shipping in fog

A foghorn or fog signal is a device that uses sound to warn vehicles of navigational hazards such as rocky coastlines, 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.

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