ELI5: Explain Like I'm 5

Hydrophone

A hydrophone is a special type of microphone that we use to hear underwater. It works the same way a regular microphone does, by picking up sound waves and sending them to a speaker. However, it works better underwater because it is designed to be able to capture sound waves that travel underwater, which regular microphones can't do. It is used a lot by scientists so that they can listen to the sounds made by whales and other sea animals.