First Alert CO250B Carbon Monoxide Detectors, WhiteHighlights: Battery Powered Electrochemical Sensor Color : White Single station carbon monoxide alarm specifically designed for residential and institutional applications including sleeping rooms of hospitals, hotels, motels, dormitories, and other multifamily dwellings Provides early warning of the presence of carbon monoxide It features an electrochemical carbon monoxide sensor, an 85dB horn, a 9 volt battery power supply, a full function test