The Fisher Labs XLT17 Liquid Leak Detector with Multi-Sensor is designed for locating leaks in all types of surface conditions and has superior leak detection capabilities in an extremely compact design. The Multi-Sensor component provides better sensitivity to leaks, improves audio clarity, improves sensor electronics, and reduces interfering background noise.The XLT17 liquid leak detector finds leaks in four easy steps: by electronically amplifying leak sounds, selectively filtering out noise, isolating the leak sound, and leading the operator to the source of the leak. A leak can be detected 6-8 feet down and as much as 50 feet away. The closer to the leak, the louder the audio signal. Search for leaks in PVC pipes in the lower frequency ranges and for cast iron and steel pipes, use a higher frequency. The included headphones are designed to deliver the clearest sound with the least distortion.