The north pier lighthouses, built in 1907, guide ships to this port. The inner light replaced a smaller wooden lighthouse that had been in use since 1847, and after the north pier was extended the outer light tower was added, allowing mariners to find the harbor entrance by aligning the two lights. St. Joseph is one of only two Great Lakes harbors with such a range light system. The inner lighthouse also contained foghorn equipment that sent out a distinctive signal to aid navigation. During periods of high waves or icy conditions, lightkeepers used the steel catwalk to reach the lights. The 1847 wooden lighthouse served the harbor for more than half a century, and an attached building added in 1896-1897 housed a steam-powered fog horn before both structures were replaced by the current inner pier light. A Fresnel lens in the inner pier light represented a tremendous advancement in lighthouse technology, using special arrangements of glass prisms to increase the distance the light could be seen by more than five times and to project its beam up to 17 miles.