This balanced, passive hydrophone is perfect for ultra low-noise, high-gain recording. Made with shielded black cable, a large 35mm brass piezoelectric head coated in black non-toxic rubber, and a male XLR output plug. Can be used for all kinds of underwater listening and recording, including detecting swimming pool leaks. Can also be used outside of water as a normal contact microphone. Can be safely frozen or boiled. Use with an amplifier for best results. Extremely rugged!