The First Alert Cat. No. CO605B is a direct plug-in, 120V AC, 60Hz single station carbon monoxide alarms specifically designed for residential and institutional applications including sleeping rooms of hospitals, hotels, motels, dormitories and other multi-family dwellings as defined in standard NFPA 720. CO605B complies with UL2034, NFPA 720 and other agencies that model their codes after the above agencies. CO605B meets codes where plug-in AC with battery backup carbon monoxide alarms are required. First Alert CO605B features an electrochemical CO sensor, an 85dB horn, End of Life and silence features, a single button for test/silence and an LED power indicator. The low power warning indicator will cause the alarm to chirp? when the battery needs replacing. The low power warning indicator can be silenced for up to 8 hours. CO605B can be plugged directly into an outlet.