First Alert 3 in 1 Explosive Gas and Carbon Monoxide Alarm 3-in-1 DC plug-in detector protects against carbon monoxide, methane and propane gas Easy-view backlit digital display shows current and peak carbon monoxide levels in your home Battery backup provides added safety during power outages (2 AA batteries included) Test/silence button ensures your detector is functioning properly for constant protection from combustible gases ETL safety listing demonstrates this product has met minimum requirements of widely accepted product safety standards