Diaphone

As this low-frequency sound could carry farther, Northey's son Rodney redesigned the "Type F" model to sustain the second low tone,[7] creating the familiar two-tone fog signal, commonly used in lighthouses and lightvessels in the United States and Canada (as well as in a famous series of radio commercials for Lifebuoy soap).

[8] Rodney Northey sold the Diaphone Signal Co. in 1932, when it was bought by a Buffalo, New York company, Deck Brothers, working under contract for the United States Lighthouse Service.

The European manufacturing rights were obtained by Chance Brothers of Birmingham in the United Kingdom, already a major supplier of Fresnel lenses and other equipment to lighthouse authorities.

This was partly a result of automation of lighthouses, but it was also found that modern diaphragm horns would produce similar levels of volume to a diaphone while requiring much smaller and less powerful compressors.

This considerably smaller device was produced by the Gamewell Corporation, of Newton, Massachusetts, for use as a municipal alarm, especially at fire stations, to alert firefighters and the public during emergencies.