||In traditional radio-based localization methods, the target object has to carry a transmitter (e.g., active RFID), a receiver (e.g., 802.11x detector), or a transceiver (e.g., sensor nodes). However, in some applications, such as safe guard systems, this precondition cannot be assumed. In this thesis, we propose a model of signal dynamics to allow tracking of transceiver-free objects. Based on Radio Signal Strength Indicator (RSSI), three tracking algorithms are proposed to eliminate the noise behaviors and improve the accuracy. The midpoint and intersection algorithms can be applied without calibration, while the best-cover algorithm requires calibration. Our experimental test-bed is a grid sensor array based on MICA2. The experimental results show that the best side length between sensor nodes in the grid is 2 meters and the best-cover algorithm can reach localization accuracy to 0.99m.