Abstract. Determining physical location of indoor objects is one of the key issues in ubiquitous computing. Although there are many proposals to provide physical location tracking, those have some restrictions such as a dependence on the type and size of objects and a trade-off between position accuracy and the number of sensing devices. In this paper we present a hierarchical approach to conquer these restrictions using mobile detectors. We describe a system called MobiTra that estimates the position of indoor any and all objects using mobile detectors’ detection histories. The effect of position estimation is evaluated through prototype testbed and simulation. 1 Intoroduction Determining the location of indoor objects is one of the fundamental issues in ubiquitous computing. The importance and promise of location-aware applications has led to the design and implementation of systems for providing location information, particularly in indoor environments where the Global Positioni...