This paper discusses the design and implementation of ESSPL, an expert system which generates security plans for alarm systems (Figure 1). Security planning is the task of determining an ecient layout of sensors, alarms, and the associated wiring for a building. ESSPL uses Rule Based System technology to generate a plan and Constraint Based technology to position the alarm equipment. A Constraint Logic Programming Language (CONTA) is developed to solve the positioning problem. ESSPL proved to be an excellent tool in automatic planning in laboratory tests. Field tests were also carried out and examined whether there is a drawback to use ESSPL in the real world context. This is also discussed in this paper. Problem Description SECOM Co., Ltd. is the leading security service company in Japan, providing alarm system services to more than 400,000 subscribers over the country. When a sensor detects an abnormal situation, the alarm system sends a signal to the central monitoring station. A t...