Passive sonar is a technology used to detect and locate underwater objects, such as submarines or marine life, by listening for sounds. Unlike active sonar, which emits sound waves and listens for their echoes, passive sonar relies on the natural sounds produced by objects in the water. This makes it less detectable and allows for stealthy monitoring. Passive sonar systems typically use hydrophones, which are underwater microphones, to capture sound waves. These sounds can include engine noises, propeller sounds, or even the calls of marine animals. By analyzing these sounds, operators can determine the location and movement of various underwater entities.