Abstract: A system for detecting small leaks at low pressures in hermetically sealed units that includes a first flow circuit for connecting a test unit to a source of pressurized gas (air) to place the unit at a desired test pressure. The gas (air) is then rerouted through a second flow circuit containing a bubble chamber so that in the event of a leak, a stream of bubbles are produced in a liquid. The presence of bubbles in the liquid is detected by a doppler radar which provides an alarm signal in response thereto. The mass displacement of the bubbles within the liquid is controlled and the time period between bubbles is sensed to provide sufficient data to quantify the leak rate.