What a carbon monoxide alarm is for, the standard it should meet, and the principles of where to site one.
Carbon monoxide cannot be seen, smelled or tasted, so a correctly chosen and sited carbon monoxide alarm is an important back-up that can warn occupants when an appliance is producing it.
The first point is the right type of alarm. An audible carbon monoxide alarm intended for the home should meet the recognised standard for such alarms, BS EN 50291, so fit one designed for the purpose rather than relying on a cheap or unbranded device.
The second point is that an alarm is a back-up, not a fix. It does not make an appliance safe, and it does not replace adequate ventilation, a sound flue, correct combustion or routine servicing. It buys warning time if something goes wrong.
Siting follows the alarm maker instructions and current guidance. The general principles are to place an alarm where it can sense carbon monoxide from the appliance and where it can be heard by the people it protects, while keeping it clear of positions where its reading would be distorted, such as right next to a flue, in dead air, or where it would be obstructed.
Upkeep matters as much as fitting. Alarms have a service life and a test button, so occupants should test it regularly and replace it at the end of its stated life, because an alarm past its life or with a flat cell gives false reassurance.
When you advise a customer, frame the alarm correctly: a useful last line of defence that complements safe appliances and good combustion, fitted and maintained to the maker instructions and the current guidance, not a reason to skip servicing.