Detectors can be powered two ways:
Batteries: These are the easiest to install. They require no outlets or wiring connection, however, batteries must be replaced twice a year. We recommend you change them in the spring and in the fall when you change your clocks. All UL listed battery operated detectors are required to sound a trouble signal when a replacement is needed. The signal usually lasts 7 days, so it's advised to check the efficiency of the detector following extended periods away.
Household current: Detectors can be powered with household current two ways. They can be plugged into any wall socket or can be wired permanently into your home's electrical system. Some may also have a battery backup