The fog horn building shows the sound signal system installed in 1903 plus its history.

Since light cannot be visible a long distance in bad weather conditions a sound signal must be added to the light transmitted by the lighthouse. In the beginning there was a cannon at Point-au-Père that was fired every half-hour once the weather conditions and visibility warranted it, later (1894-1903) it was replaced by an explosive signal given every 20 minutes.

In Spring of 1903 this was replaced by a Scotch Siren, a British invention at the end of the 19th century. This necessitated the building of a hangar about 120 meters (400’) NE of the Lighthouse to shelter the fog horn. The Horn was situated outside the hangar and was 5.5 meters (17’) above the high tide mark. and was mounted on rails in a half circle to permit maximum effect in all wind conditions.

In 1904, the siren was replaced by a diaphone operated by a Fog-signal engineer. By modifying the Scotch Siren a Toronto manufacturer had newly invented the diaphone.This worked with a rotating cylinder and an alternative piston on the diaphone. The piston was activated with compressed air keep in three large tanks and charged by a gas motor. The energy source to the horn gave a three seconds of sound followed by three seconds of silence then three more seconds of sound with a fifty one seconds of pause before the next signal. To improve the signal the horn was moved to the top of the building, then to a small tower and finally to the top of the lighthouse. An under ground pipe was used for the air.

In 1972, Transport Canada automated all aids to navigation therefore ceasing the operation of the diaphone and replacing it with an electronic whistle with less power in the Spring of 1996.