Carbon Monoxide detectors are all the same on the inside, so there is less of a debate here. CO detectors are available in several different varieties, and they can have additional functionality, like explosive gas detection in addition to CO detection. They can be wall-mounted, outlet-mounted, stand-alone units, or included as part of a dual-sensor smoke and CO alarm. Heat rises, and CO is associated with heating appliances, as it is most commonly encountered as a product of incomplete combustion. Additionally, on a molecular level, CO is slightly lighter than air. The EPA recommends wall-mounted units about 5 feet from the floor. But ultimately, the best CO detector for you and your family is one that works, has fresh batteries, and that is less than 7 years from its date of manufacture.