Compact and lightweight, non-invasive apparatuses to determine tissue wetness/hydration based on the frequency responses of regions of the tissue below a sensor of the apparatus. Described herein are compact and lightweight apparatuses having a sensor with an array of electrodes that is directly connected or connectable to control circuitry to attach to the back of the sensor, which can be worn by a patient. The control circuitry may include a multiplexer (MUX) coordinating the reciprocal selection of drive and sensing electrodes, and a one or more constant current sources. Methods of using these devices to detect tissue wetness are also described.
