This European Standard specifies general requirements for the construction, testing and performance of electrically operated carbon monoxide gas detection apparatus, designed for continuous operation in domestic premises. The apparatus may be mains or battery powered. Such apparatus is intended to warn of an accumulation of CO, enabling the occupant to react before being exposed to significant risk. Additional requirements for apparatus to be used in recreational vehicles and similar premises are specified in EN 50291-2. NOTE For caravan holiday homes EN 50291-1 applies. This European Standard specifies two types of apparatus, these are - type A - to provide a visual and audible alarm and an executive action in the form of an output signal that can be used to actuate directly or indirectly a ventilation or other ancillary device, and - type B - to provide a visual and audible alarm only. This European Standard excludes apparatus - for the detection of combustible gases, other than carbon monoxide itself (see EN 50194-1), - for the detection of CO in industrial installations (see EN 45544-1, EN 45544-2 and EN 45544-3) or commercial premises, - for CO measurement for smoke and fire detection.