The use of wireless sensor networks to protect sensitive facilities or international borders has recently attracted more and more attention [1-3]. It has become a highpriority issue in many countries. In addition to the physical fences built for stopping illegal intruders from crossing the border, smart fencing has been proposed to extend intrusion detection capabilities. Event detection is a central component in numerous wireless sensor network (WSN) applications [4, 5]. In spite of this, the area of event description has not received enough attention. The majority of current event description
approaches rely on using precise values to specify event thresholds [6, 7]. However this crisp values cannot adequately handle the imprecise sensor readings. Therefore, In this paper, Event-detection algorithm based on two layers fuzzy Logic
system (FLS) is used, which conveys the idea of using fuzzy values instead of crisp ones which significantly improves the accuracy of event detection. Each sensor node has an acoustic signal sensor and one-axis acceleration sensor to improve the precision of the detection system, as well as reducing false alarm rate specially in a noisy environment.