The aim of this research is to develop a method that would allow to effectively detect active intruder's attacks using network traffic and physical features analysis for wireless sensor network (WSN) nodes. We analyze the physical characteristics of potential target nodes, and then design a method for malicious node identification in cases of physical features violations. The proposed method is based on the use of probabilistic functions, confidence interval calculation and finding the probability of deviation of observed parameters from the confidence interval. The novelty of the method is because we estimate the probability of observation fitting into the confidence interval and not compare with the sample distribution. In addition, the proposed method allows detecting a malicious node according to its physical features, while most intrusion detection systems (IDS) deal with the network traffic. The advantage of the proposed approach is also supported by the fact that there is a chance of attacks against physical activity (e.g., node movement disorders, power depleting, communication noises, etc.).