Leak detector apparatus comprising a sensor which can be clamped on a vacuum or pneumatic pressure line to detect the presence of a leak in the line near the clamping location, and an indicator coupled to the sensor to indicate the intensity of signals transmitted by the sensor. The sensor includes a transducer formed of piezoelectric material for transducing to an electric signal the low-amplitude, high-frequency random-force component applied to the clamping surfaces by the turbulence noise which results from the leak. Certain embodiments of the apparatus have a sensor which also includes a mechanical resonator for amplifying the electrical signal that is transmitted.