Just as microphones are used to listen to sound in air, devices called hydrophones are used to listen to sound underwater.
Microphones convert sound in air into electrical signals. The electrical signals can then be amplified, recorded, played back over loudspeakers, and transmitted over telephone lines.
The electrical signals can also be used to measure the characteristics of the sound, such as amplitude and frequency.
Similarly, hydrophones convert sound in water into electrical signals that can be amplified, recorded, played back over loudspeakers, and used to measure the characteristics of the sound.
