Methods and devices for measuring blood flow velocity are provided. The device may include a wave source and at least two detectors positioned along a blood vessel. The wave source, which may include an ultrasound transducer or a mechanical source, is configured to induce a pressure wave in blood flowing in a blood vessel. In one example, the detectors are both positioned downstream of the wave source, with respect to the direction of blood flow. In another example, one detector is positioned upstream of the wave source, and a second detector is positioned downstream of the wave source. The difference in time it takes for the induced pressure wave to reach the first and the second detectors is indicative of the velocity of blood flow in the vessel.