In this paper, we demonstrate a novel tag-free indoor tracking system using received signal strength indication (RSSI) measurements. While most indoor tracking and monitoring systems require a person to carry a transmitter/receiver device or tag, our approach requires no such tag, and works unobtrusively in the background. The approach is based on the key principle that radio frequency (RF) signals between wall-mounted transceivers reflect and absorb differently depending on a person's movement within their home. Classification algorithms detect disruptions in the RF signals to determine region based localization and activity of the person. Preliminary experiments show 2-3 meter equivalent localization accuracy and the ability to discriminate whether one or more people are present in a room. While the proposed system is being developed for long-term monitoring of elderly within their home or health care setting, the approach is applicable to a variety of ubiquitous computing and tracking applications where passive tag-free tracking is desired.