This paper discusses the design and implementation of ESSPL, an expert system which generates security plans for alarm systems. Security planning is the task of determining an efficient 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.