The article presents a general method for identity the security risk factor for alarm signal transmission systems (ASTS), which are used in monitoring buildings and critical infrastructure. The security of the transmission of alarm signals to an alarm receiving center (ARC) is a property of the process, which is associated witch performing of tasks and functions, human factor, hardware and environment components. The process of transmitting alarm signals should be characterized by minimizing risk of external and internal interception/distortion or deformation of transmitted signals and in ideal case signals should be encrypted and integrity checked. Determining the security risk indicator for ASTS will allow optimal organization of electronic security systems.