The "Denver Quadruplex" was a very early example of an electric siren, first invented and sold in 1914. The company who built these, the Denver CO-bssed William A. Box Iron Works Company , is generally credited for inventing the first practical electric outdoor warning siren, the Denver Type A, a few years earlier. Surprisingly, several of these remain in service today despite being 90-110 years old. These were originally meant for use in mines, but later found popular use as fire sirens. While manufacturered by William A. Box, the sirens were typically sold through vendors such as Hendrie & Bolthoff.