AC/DC, Plug In, Dual Power Carbon Monoxide Alarm, Alerts You To Dangerous Carbon Monoxide, Dual Power System With Battery Back Up For Continuous Monitoring, Even In The Event Of A Power Outage, The Backlit Digital Screen Tells You At A Glance What The Carbon Monoxide & Power Levels Are, Features A Convenient Test & Silence Button & An End Of Life Timer That Lets You Know When It Is Time To Replace The Unit, Electrochemical Sensor Type.