SONAR uses sound waves to detect obstacles in water. It was invented in 1906 and is used by navies and whales. Active SONAR sends out sound waves and detects echoes to accurately map locations, but reveals the user's position. Passive SONAR listens for other sound waves without emitting any, making it better for stealth but less accurate unless combined with triangulation. While effective for mapping underwater, high-powered naval SONAR can damage cetaceans' hearing and cause hemorrhaging.