A system and method for sensing a user presence via thermal signature sensing employs adaptive filtering of a motion spectrum to discern a user presence signature over background thermal noise. In an embodiment, adaptive sub-band filters are applied within the motion spectrum, and a user presence is indicated by the presence of a thermal signature having at least a predetermined magnitude or profile within any searched sub-band. In an embodiment, a low pass filter is applied to search for a stationary presence if the sub-band search procedure does not yield a user thermal signature.