This chapter discusses the electronic alarm systems, focusing on design concerns and selection issues. The alarm system with its associated sensors should detect an intruder as early as possible. This requires both exterior and interior sensors. The electronic alarm system collects the sensor inputs and provides the alarm and location information to the operator in the security control center (SCC). The goal of a security program is to provide cost effective detection, assessment, delay, and response. A properly designed alarm system provides the first component goal, which is detection. For the corporate security professional, there is a strong interest in utilizing systems that communicate on Internet Protocol (IP) based architecture. The push has been to minimize cost by using existing IT infrastructure in the company. Developing a solid alarm philosophy requires an understanding of the functional requirements. These requirements are developed by understanding the security vulnerabilities, the business risks, the appropriate levels of protection, and the key assets and threats.