Consider a security system that is an extended version of the system shown in Figure 2.6, which is intended to protect against intrusion and to detect fire. It incorporates smoke sensors, movement sensors, door sensors, video cameras under computer control, located at various places in the building, an operator console where the system status is reported, and external communication facilities to call the appropriate services such as the police and fire departments. Draw a block diagram of a possible design for such a system.