An aspect of the invention is a liquid sensor having a galvanically energizable power source capable of activating a remotely detectable signal in response to liquid. In a preferred embodiment, a liquid sensor includes a plurality of electrodes, a circuit, and a transmitter thereon. The electrodes are coupled to generate electrical power when in contact with liquid. The circuit is electrically connected to the electrodes so as to be activated by the electrical power, detect an electrical parameter of the electrical power, and generate a plurality of data packets indicating a degree of wetness corresponding to the detected electrical parameter. The transmitter is electrically coupled to the circuit to receive the plurality of data packets and transmit representations of the plurality of data packets as electromagnetic signals. Other aspects include a liquid absorbent wetness sensor and a computer-based wetness monitoring system, and method of detecting liquid.