Carbon monoxide (CO) is such a fearsome poison because it has no odor and it can enter almost any home. Also, CO poisoning is difficult to diagnose because many of the symptoms of low- to mid-level exposure mimic a large array of other ailments, such as the flu. The gas forms from malfunctioning combustion appliances such as generators and furnaces. The vast majority of exposures do not result in permanent injury, although temporary ailments, such as headaches and nausea may result. The best defense against CO is strategic placement of CO detectors. To find out more about detector placement, CO dangers and sources, check out our new article on carbon monoxide.