Recent experiments at Brookhaven National Laboratory and Harvard University demonstrate that a detectable sonic signal is produced by energetic proton beams traversing fluids. The novel results are in agreement with the predictions of a thermal expansion model of the generation of the acoustic wave. They are inconsistent with any significant contributions from either microbubble implosion or molecular dissociation. Frequency and amplitude distributions, radiation patterns, and temperature, pressure, and medium dependences are explored. This phenomenon may have immediate applications as a beam monitor and as a detector of energetic heavy ions. Signal thresholds may be low enough to permit detection of particle showers induced by single particles at the next generation of high energy accelerators or from high energy cosmic rays. The inexpensive transducers and long sonic transmission lengths obtainable in liquids suggest that high energy particle detectors may be feasible with masses many orders of magnitud...