Audible systems were used when keepers needed a warning device when visibility was poor. The first fog signals in Lake Huron and Georgian Bay area began with hand driven horns.
Later, fog horns were developed using steam, and other compressors to move the air to create a low sound which travelled further across the water.
The diaphone fog alarm was invented by Professor John Pell Northey of Toronto University. To manufacture the new equipment, Northey set up the Diaphone Signal Co. at Toronto in 1903. The Diaphone had a characteristic “grunt” at the end of its reverberation. Flower Pot, Cabot Head and Cape Croker lightstations all used this type of fog alarm, which required a separate out-building.
Some of the Fog Horns at Bruce County light stations are still in use today.