Abstract: In one embodiment a water leak detector and alarm unit senses sounds in the vicinity of a plumbing fixture, such as a toilet or sink. The characteristics of these sounds are used to determine the presence of a water leak and discriminate between a leak and normal water usage sounds. The unit comprises a microphone (105), electronic circuitry (110), a loudspeaker (115), an optional lamp (140), and an optional battery (120) or power supply (150). Signals from sound sensed by the microphone are amplified by an amplifier (400), and filtered by a filter (405) before being passed through a detector (410), an integrator (415), and a level discriminator (420). The discriminator quantifies and separates sounds into three categories: background, leak, and normal water usage levels. A particular signal is ascribed to each category. These signals are fed to a logic unit (425) for analysis and possible activation of an alarm (115).