3MK-CO220 Carbon Monoxide Detector Mains & Rechargeable BatteryWhen 3MK CO220 Carbon Monoxide Detector detects potentially dangerous level of Carbon Monoxide , it will flashes RED alarm light immediately and sounds a loud alarm if the carbon monoxide persists. At higher levels of carbonmonoxide alarm turns on sooners. The rate of flashing of the Red light indicates the level of Carbon Monoxide. 3MK CO220 Carbon Monoxide Detector checks for carbon monoxide every 50 seconds. 3MK CO220 Carbon Monoxide Detectors are