The defensive elements of a protective system can be assembled in four steps: determining response time, identifying defensive layers, establishing delay times of those layers, and comparing delay time to response time. A reasonable response time is the basis for the defensive phase; once it is established, the layers of building elements that can delay an intruder are created. Three defensive layers are generally established in a building: a safe, the interior room surfaces, and the exterior building surfaces. Delay times of any defensive layer is limited to the shortest delay time of its individual components; delay times differ between types of layers. A comparison of response time and delay time will determine whether the existent protective system is sufficient. The detection phase, which will set up the intrusion detection system, is interdependent with the defensive system and will easily follow it. Detection must occur before an intruder breaches a defensive layer for that layer's delay time to be counted. It is imperative that the location and type of sensor be chosen carefully and correctly. Assessment systems are used to verify alarms; those that are keyed to the detection system must assess the presence of intruders where sensors are activated. Assessment system equipment must also be carefully selected and lighting requirements established in order to enhance operator confidence in the protective system. 4 figures.