This paper aims to develop a smart building-security system utilizing fog technology. Fog computing is an innovative solution to reduce latency and network congestion, in which the cloud is extended to the edge of the network. The proposed system can detect an intruder, fire and water leakage. It is implemented using Raspberry Pi, Arduino, Pi-camera and different sensors. The sensors are installed on Arduino and Pi-camera is mounted on Raspberry Pi. The Raspberry Pi is used as a fog node to fit the time-sensitive nature of the system. The performance was evaluated through the iFogSim toolkit. Fog reduces 33.26 and 46.8% average latency and sensor delay as compared to the cloud. Also, the value of the network usage decreases by 71% in the case of fog-based even with increased network load. Finally, the iFogSim was evaluated by measuring the simulation time, which gave acceptable results of about 8.5 sec.