This invention is an intruder detection system which integrates wireless sensor network and security robots. Multiple ZigBee wireless sensor modules installed in the environment can detect intruders and abnormal conditions with various sensors, and transmit alert to the monitoring center and security robot via the wireless mesh network. The robot can navigate in the environment autonomously and approach to a target place using its localization system. If any possible intruder is detected, the robot can approach to that location, and transmit images to the mobile devices of the securities and users, in order to determine the exact situation in real time.