A hydrogen sensor is reported in which a small piezoelectric-sound-resonance-cavity (PSRC) is used as the sensing element. Detection utilizes sound resonance and acoustic property differences between H-2 and air as a sensing mechanism. Changes in H-2 concentration result in a shift of the sound-resonance state of the PSRC. Preliminary experiments have demonstrated a sensitivity limit of 8 ppm, a fast response time similar to1.5 second, and detection capabilities over a broad concentration range 10(-5) < n < 0.2. (C) 2003 American Institute of Physics.