Abstract: A device for detecting and locating leaks in pipelines through which a stream of fluid flows under pressure. The device includes an elongate body portion providing support for axially spaced sets of plural radially extending baffles, fore and aft of the stream and of a diameter less than the inside diameter of the pipe to be probed; and an intermediate portion including a differential pressure measuring device and recorder which forms with the inner pipe wall, a chamber normally maintained at the stream pressure as the device is propelled through the pipe at the speed of fluid flow. As the device passes a leak fluid pressure in the chamber is reduced due to the substantial isolating affect of the baffles from the up and down stream pressures with a resultant recording indicative of the leak location, while eliminating the need of totally sealing off the chamber.