The success of Wireless Sensor Network application monitoring relies on the accuracy and reliability of its nodes operation. Unfortunately, operation deviations of these nodes appear as regular occurrences not isolated events as in traditional networks. This is due to their special characteristics that reduce network manufacturing and deployment costs and maintain the nodes immunity against internal and external conditions. The goal of this chapter is to propose a real-time, distributed, passive, and low resources usage performance-monitoring algorithm that monitors Wireless Sensor Network functionality and isolates the detected deviated nodes from norm operation. Simulation and empirical experiments showed that the proposed algorithm has a slight processing and storage overhead. It is important to mention that these experiments showed that the proposed algorithm has a high reliability in tracking and isolating network nodes problems.