a telephone that operates entirely from
electricity generated by the speaker's voice, with no external
power supply or
battery. When a person speaks into such a phone, the
sound waves of his voice
cause a
special device within the transmitter to vibrate and generate the current needed to operate the phone. At the other end of the
line, the receiving
unit operates on the same principle, taking the
signal and translating it back into
speech.
Sound-
power telephones are commonly used on ships and due to their simplicity are rugged, reliable and easy to
repair.