With the prevalence of Wi-Fi activity within a wireless network, there are growing interests in mobile surveillance and device tracking for better network services. With a good location estimation algorithm integrated into a wireless network, system administrators can closely monitor the network traffic as well as the behavior of the mobile users. By modifying the embedded software in off-the-shelf WLAN APs, our system can sniff out data packets transmitted by WLAN devices without the need to install client programs on mobile user devices. In this paper we propose the Aggregated Signal Layout location estimation algorithm. Experiment results show that once wireless activities had been detected, our signal strength based localization algorithm can estimate positions of the wireless mobile devices involved with great success rate and good accuracy. With an accuracy comparable to the fingerprinting method but without paying the high costs of training and maintenance of the fingerprint databases inside our WLAN system, the proposed Aggregated Signal Layout method is well-justified for its efficiency and effectiveness in locating and tracking mobile users' activities within a wireless network.