Carbon monoxide is an odorless, colorless and toxic gas. Because it is impossible to see, taste or smell the toxic fumes, CO can kill you before you are aware it is in your home. At lower levels of exposure, CO causes mild effects that are often mistaken for the flu. These symptoms include headaches, dizziness, disorientation, nausea and fatigue. The effects of CO exposure can vary greatly from person to person depending on age, overall health and the concentration and length of exposure.

 
Here are some tips to reduce exposure to carbon monoxide:
-Keep gas appliances properly adjusted.
-Consider purchasing a vented space heater when replacing an unvented one.
-Open flues when fireplaces are in use.
-Have a trained professional inspect, clean, and tune-up central heating system (furnaces, flues, and chimneys) annually. Repair any leaks promptly.
-Do not idle the car inside a garage.
 
More carbon monoxide information can be found at http://www.epa.gov/iaq/co.html