Invisible and odorless carbon monoxide gas kills over 5,000 people each year. Clogged chimneys, malfunctioning stoves, water heaters, space heaters, as well as auto, boat and airplane exhausts release carbon monoxide into the air that you breathe. The PRO-LAB® DO IT YOURSELF CARBON MONOXIDE TEST KIT contains two (2) yellow chemical buttons that turn grey when in contact with carbon monoxide. They will detect as little as 50 ppm (before it becomes dangerous to you and your family.) The instant detector is reusable and, once opened, each button will last up to three (3) months.