"CO" stands for carbon monoxide, a colorless, odorless gas that can be very dangerous. It is produced when fuels like gasoline, wood, or natural gas are burned incompletely. Because it is hard to detect without special equipment, carbon monoxide can build up in enclosed spaces, leading to poisoning. Symptoms of exposure include headaches, dizziness, and confusion. To stay safe, it's important to have carbon monoxide detectors in your home, especially near sleeping areas. If the alarm goes off, you should leave the building immediately and call for help. Regular maintenance of heating systems and appliances can also help prevent CO buildup.