Carbon monoxide is a killer. That’s why CO checks need to be carried out when a gas heating or boiler is being serviced or installed. The compact testo 317-3 CO meter is designed to provide you with a quick and reliable means of testing the surrounding air for carbon monoxide. Carbon monoxide is a particularly dangerous gas. It is colorless, it is odorless and above all it is lethal. That`s why it is so important that CO checks are carried out by the book when a gas heating or boiler is being serviced or installed. This not only ensures that the heating or boiler is working properly, it also helps to prevent tragic accidents that occur as a result of carbon monoxide poisoning.