A system for sensing human activity by monitoring impedance includes a signal generator for generating an alternating current (AC) signal, the AC signal applied to an object, a reactance altering element coupled to the AC signal, an envelope generator for converting a returned AC signal to a time-varying direct current (DC) signal, and an analog-to-digital converter for determining a defined impedance parameter of the time-varying DC signal, where the defined impedance parameter defines an electromagnetic resonant attribute of the object.
