HY 200 Hydrophones make the SeCorr A200 an excellent measuring system for use along large pipelines and long distances between RT 200 radio transmitters. HY 200 Hydrophones are installed directly into the water column rather they do not use noises on the pipe structure, rather they use the noise in the water column which travel much farther. HY 200 hydrophones are extremely sensitive in the low frequency range, far below audible sounds. This makes the HY 200 a perfect compliment for systems that are predominately plastic. The HY 200 hydrophones kit includes a tough constructed carry case.