CO detectors come in a variety of shapes and sizes. Some are table-top battery-operated units. Some have digital readouts of CO levels. Others plug into wall outlets and don't require batteries. You can even get a combination smoke and CO detector. The variety isn't important - that you have one is.

CO detectors monitor the air composition in a room. When the detector notices high levels of the gas, it sounds - similar to a smoke detector.

- Install your smoke at least 15 feet away from a gas-combustion appliance. Only install plug-in detectors in sockets that aren't controlled by light switches.

- If you only use one CO detector, mount it in a hallway near the sleeping area, so that it will wake you if high levels are reached at night. Because a molecule of CO is roughly the same weight as other air molecules, they float freely around the room. You can install a detector anywhere -- near the floor, on a desktop, or from the ceiling -- unlike a smoke detector, which should be mounted at the highest point in the room.

- CO detectors should be cleaned and checked when you inspect your smoke detectors.