Fire systems are composed of two basic but distinct functional areas. One is the plumbing/mechanical side and the other is the electronic side. This chapter discusses both the aspects of a typical fire system but primarily focuses on the electronic side. Fire and emergency response is important to every security professional. Monitoring these systems may or may not be the part of the security control center (SCC) function; however, the response and evacuation systems are part of the security tasks. Therefore, it is important to understand the inner workings of a fire alarm system. By explaining the physical piping, sensors, and electronic panels, the mystery as to why these systems sometimes cause false evacuations in the buildings is addressed in the chapter. The sprinkler system extinguishes fire. The concept of a sprinkler system is simple: fires develop heat that rises; when that heat reaches the same temperature as the sprinkler head rating, the fusible link in the sprinkler head melts and the water is released.