A perimeter intrusion alarm system consists of four interactive functions: (1) delay, which consists of a fence or wall to slow the escape; (2) detect, which picks up the intrusion alert; (3) alert, which sounds the control center alarm and identifies the alarm location; and (4) respond, which dispatches officers to the alarm area. There are two types of intrusion alarm systems: the mechanical system which must be physically tripped, and the type that is triggered by disturbances in an invisible barrier or energy field. All intrusion detection systems are composed of sensors, signal processing unit(s) and display and verification equipment. No matter which system is used, the security logic is always the same. The sensor creates a signal that is sent to a central processing unit where it is displayed, verified, and acted upon. High-tech security systems must be evaluated carefully, for a thorough evaluation helps to determine the appropriateness of a product for a specific facility.