An Home Emergency Power System doesn't simply back-up your power.
it backs it up automatically. Even when you are not at home.

Each system includes an automatic transfer panel and generator. It works like this:
the automatic transfer panel senses when your electricity is out and activates your generator, which produces the power you need. When your regular electricity returns, it automatically switchess back to your main supply. The generator can be hooked up to your existing natural gas line or propane tank.