Simply put, an ATS is a switch that automatically transfers power between two sources. Why do you need one? When your power goes out, the last thing you want to do is scramble for a flashlight or lantern to find your way to the generator, then start up the generator. WIth an ATS installed, you don't have to lift a finger. When the outage hits, the ATS does the work for you. The power switches to your generator within seconds, letting you carry on with your life. And when the power comes back on, the ATS automatically switches your power back.