The article presents basic issues associated with the power supply of integrated electronic security systems (IESS) operated in various facilities. Ensuring the reliability of an IESS power supply is an important issue associated with the operation of these systems that are responsible for the safety of people, accumulated property, natural environment, and cooperating structures—e.g., storage facilities. IESSs are operated under harsh external or internal environmental conditions. In such a case, we are dealing with processes of beneficial or adverse impact, which actively affects IESS operation. The IESS operation process is also associated with ensuring power supply continuity under normal operating conditions. This also means ensuring transition to backup power supply systems in the event of failures. Therefore, an IESS should exhibit high reliability related to the power supply process. To this end, the article presents two representative IESSs operated in buildings and in a vast area. The analysis covered the processes of power supply from basic energy sources (BES) and backup sources in cases of failures. The further segment of the article describes developed models of these power systems with acceptable and unacceptable technical states associated with an IESS power supply. The last section of the article defines a model and graph of a selected IESS operation process and describes a conducted computer simulation associated with operational safety. Such an operation process analysis enabled drawing conclusions that can be utilized throughout the entire IESS operation process.