First Alert® plug-in carbon monoxide alarms are designed to be easy to install, easy to maintain, and quality-engineered for years of virtually maintenance-free service. The full line includes some models with special features like silence buttons, digital display readouts and line cord for easy positioning of alarm. Below are the features all First Alert® carbon monoxide alarms share. Plug-in carbon monoxide alarm with 9V battery backup meets most state and local codes for carbon monoxide alarms.