The device indicates e.g. inhalation and/or exhalation air flow rate by providing a plurality of corrugations extending into the fluid flow path, allowing at least two sound signals to be produced at e.g. different resonances for e.g. flow rates at 50L/min separations. Corrugations possibly run 50-300mm in axial length may be formed integrally surrounding the flow in an e.g. plastics body and/or positioned in a recess. Each corrugation ridge may have asymmetrical cross-section, producing e.g. inhalation/exhalation sounds of different frequency. The sound signal may be analysed on e.g. a mobile phone app to provide healthcare feedback, or providing an alert. Potentially used as a spirometer, the flow meter has no moving parts and does not requires periodic calibration. Also disclosed is a device suitable for indicating fluid flow using at least one sound-producing corrugation in a fluid path with diameter greater than 8mm, enabling indication of typical adult respiratory flow.
