Abstract: A method and apparatus for detecting leaks in pressurized mains comprising input coupling structures spaced along a main, each coupling permitting insertion of a detector head connected to a hose/cable of extended length, a reel and housing holding the hose/cable which is designed to input fluid into the hose and make electrical connections to microphone and transducer structure in the head. Leaks in the main are located by depressurizing the main, inserting the detector head through a coupling, feeding pressurized fluid through the hose into rearwardly projecting jets in the head for effecting travel thereof lengthwise of the main, stopping the fluid flow, again pressurizing the main to effect any leaks, energizing the microphone while slowly retracting the head by winding up the hose/cable on the reel at the input position, listening for leak noise as the head is retracted toward the insertion point, and upon leak noise being heard, stopping the retraction and then energizing the transducer within the head.