This guide provides information on the selection, installation, use and maintenance of apparatus for the detection of carbon monoxide intended for continous operation in domestic premises. It should be read in conjunction with the European standard prEN 50291 together with any additional relevant national or local regulations. The guide refers to the installation of two types of apparatus: Type A apparatus - 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. Type B apparatus - to provide a visual and audible alarm only. This guide excludes apparatus. - for the detection of combustible gases (see EN 50244); - for industrial installations or commercial premises; - for use in boats, caravans or mobile homes.