Abstract: A passive device for detecting fluid flow in a pipe includes a housing, a mechanical couple for attaching the housing to at least one of the pipe and a structure disposed in close proximity to the pipe, and a chamber disposed within the housing such that the chamber is physically isolated from the pipe. The chamber is sized and shaped to receive a sound wave at a first end thereof and to amplify the sound wave between the first end and a second end of the chamber, the sound wave including a frequency range corresponding to that of a predetermined fluid flowing through an interior of the pipe. A sensor disposed at the second end of the chamber receives the sound wave amplified by the chamber, and communications circuitry is configured to send a signal corresponding to the sound wave received by the sensor to an external computing device.