Foghorns
In dense fog, the light beam might not be visible, so the lighthouse had a foghorn to alert ships. A coal-powered foghorn was installed when the light was used, but this labor-intensive system was replaced as soon as better technology was available. In 1972, the “Super Tyfon Double Fog Signal,” named after the giant Typhon from Greek mythology, was put into use. This system consisted of two compressed air horns sounding simultaneously, and could be heard up to 3 nautical miles (6 km) away. The modern electric tone fog signal was a 12 volt high frequency fog signal with a sound range of half a nautical mile. The high frequency was very effective in fog.
Read more about this topic: Point Sur Lighthouse