 Built by Trinity House in 1906, the foghorn building is a Grade II listed building. The siren was originally powered by a 15 hp (11 kW) engine, which gave two blasts in quick succession at two-minute intervals that could be clearly heard by people living on both coasts but for many years following World War II, the foghorn was heard as one long and one short blast and nautical almanac data as at 1965, stated that the interval was 1.5minutes. Volunteers from the Flat Holm Society, with help from the Prince's Trust, restored the horn and engines in the 1960s. The Foghorn Station was officially reopened by the Welsh Secretary and the Welsh Assembly First Secretary in May 2000 when the foghorn was sounded for the first time since 1988.
