The original fog signal at Souter was a single Holmes-designed reeds, housed in a foghorn house to the east of the lighthouse tower; it sounded one blast every 45 seconds and was soon replaced by a pair of twin horns facing out to sea, angled north-east and south-east.
Compressed air was piped to the foghorn from the engine room alongside the lighthouse, where the air compressor was driven by a common drive shaft from the engines powering the magnetos.
A siren replaced the reeds in February 1879.
The horns were superseded by twin Rayleigh trumpets in 1919, when a more powerful siren was installed; the foghorn house was remodelled at the seaward corners to accommodate them.
The siren signal was a 5-second sound of 480 Hz every 5 minutes.

The current pair of exponential horns dates from 1953, when a Stone Chance diaphone signal was installed.
This produced a five-second blast every 30 seconds in poor weather, up until 1988 when Souter Lighthouse was decommissioned by Trinity House.
The diaphone remains in working order and is sounded regularly for visitors throughout the year.
The original fog signal at Souter was a single Holmes-designed reeds, housed in a foghorn house to the east of the lighthouse tower; it sounded one blast every 45 seconds and was soon replaced by a pair of twin horns facing out to sea, angled north-east and south-east. Compressed air was piped to the foghorn from the engine room alongside the lighthouse, where the air compressor was driven by a common drive shaft from the engines powering the magnetos. A siren replaced the reeds in February 1879. The horns were superseded by twin Rayleigh trumpets in 1919, when a more powerful siren was installed; the foghorn house was remodelled at the seaward corners to accommodate them. The siren signal was a 5-second sound of 480 Hz every 5 minutes.
The current pair of exponential horns dates from 1953, when a Stone Chance diaphone signal was installed. This produced a five-second blast every 30 seconds in poor weather, up until 1988 when Souter Lighthouse was decommissioned by Trinity House. The diaphone remains in working order and is sounded regularly for visitors throughout the year.
Souter Lighthouse