The thermoacoustic wave generated by a sudden deposition of heat in a fluid is derived in a simple way from the fundamental laws of physics. The expression for the acoustic signal‐to‐noise ratio relative to thermal vibrations from a typical electromagnetic cascade is then developed. The signal‐to‐noise atios of several materials are compared; liquid argon appears to be one of the most promising liquids. Observation of air shower cores in a high altitude lake and cascades in an emulsion chamber are discussed as possible applications of acoustic detection.