Sound-powered telephones are widely used on ships. A typical example on a U.S. Navy ship is the "JL" circuit which is used by the lookouts to report visual contacts to the pilot house and the Combat Information Center (CIC). In this case there would be five stations on the circuit (stern lookout, port lookout, starboard lookout, pilot house and CIC).
U.S. Coast Guard Regulations require this emergency communication capability in most vessels today and dictate where phones should be located. A dial telephone system with a battery backup will not meet the USCG Regulations as they currently exist.
Other uses for sound-powered telephone technology today include emergency communications systems for high-rise buildings, draw bridges, ski lifts, and temporary locations where reliable communication is necessary. These types of systems allow for two or more parties to be able to talk to one another in areas that experience loss of power or when radio communication is hampered by RF signal losses and/or limitations.
Ski lifts use sound-powered phones extensively. Because there are only two handsets (rarely three, where there is a mid station), sound-powered phones are ideal. They are used to confirm actions of the lift with the other operator, and abnormal operation of the lift machinery.
Many different types of equipment have attempted, but have largely failed, to replace the incredibly simple sound-powered telephones on ships. Due to the rugged, reliable and power-free nature of this equipment, it remains in use on all US military vessels, commercial vessels and work boats.
