Your security system has at least one battery connected to it. This is a requirement for all systems. That battery is to keep the system operational for 24-hours should there be a prolonged power outage. These batteries are designed to last 3 to 5 years. As many folks learned during Hurricane Sandy when you are without power for several days, the system will become inoperable.
A whole-home generator is a smart idea and one of the things that many people have added to their homes and businesses to be prepared for prolonged outages. If your system is on a generator, it will continue to run and keep the battery charged. If a whole home generator isn't in the cards, there are many generator options available that cost considerably less and are easy to operate.
As mentioned, the battery/batteries connected to your system, don't last forever. The batteries last 3-5 years. The more often you have a power outage/event, the sooner they potentially will need to be replaced. We recommend that they are replaced every three years as a precaution.
Annual testing/inspection is highly recommended, and in some instances, required. In addition to batteries, other devices are not designed to operate forever and are mandated to be replaced. More on that in another FAQ about devices and "End Of Life".