Localization of sensor nodes is an essential requirement for many wireless sensor network applications. As most sensor positioning equipments are complicated and costs prohibitively high, this paper presents a low cost system based on measurements from a pedometer and communication ranging between neighboring nodes. The information is fussed through a probability-based localization algorithm. Unlike most of the existing methods that require good network connectivity, the proposed system works reasonably well in a spare network. An experimental prototype has been developed and the practical results are used to evaluate the system's performance. The results show that the system performs well.