As the temperature drops, the risk of carbon monoxide (CO) poisoning increases, linked to the use of heating appliances. Such accidents can also be caused by the use of electricity generators. Every year, France sees around 1300 episodes of CO poisoning, involving almost 3000 people. Invisible, odourless and non-irritating, carbon monoxide is undetectable. However, some simple practices can help reduce the risks. Particular attention should be paid to using mobile fuel-burning space heaters properly, and avoiding makeshift heating systems, which are particularly risky.