First Alert CO615 Carbon Monoxide Plug-In Alarm with Battery Backup and Digital Display (6 Pack) Dual Power (plug in/electric and front load battery) ensures continuous protection to make certain the alarm will work at all times, even during power outages Multi-function backlit digital screen allows you easily to see the carbon monoxide level and battery power indicators at a glance without pushing any buttons Peak Level feature displays the highest concentration of carbon monoxide measured since the unit was last reset Easily plugs into any standard outlet with no additional mounting necessary or it can also be mounted on any wall using the convenient power line cord (approx. 6 feet long) Backed by a 7-year limited warranty and meets Underwriters Laboratories (UL) UL2034 standard for safety