This Smoke And Carbon Monoxide Detector Provides 24/7 Protection. It Runs On 120V And Has A 9V Alkaline Battery Backup.FeaturesElectrochemical Carbon Monoxide SensorMore Accurate Than Other Sensing TechnologiesSingle-Button Test/SilenceLatching Alarm IndicatorRemembers Which Unit Initiated An AlarmSilencing TechnologySilences Low-Battery Chirp For Up To Eight HoursTemporarily Silences An Unwanted Nuisance AlarmEnd-Of-Life SignalProvides Audible Notification Of Alarm ReplacementIntelligent Sensing TechnologyFewer Nuisance AlarmsPerfect Mount For Easy Alarm AlignmentDust CoverEasy InstallationIt First Alert Direct Wire Ionization Smoke And Carbon Monoxide Detector, 120 Volts With 9-Volt Battery Backup