The Texas Real Estate Commission Standards of Practice recommends one smoke alarm in each sleeping room and outside each story living space.
Carbon Monoxide alarms are recommended when fossil fuels (gas/wood) are used in the home.The International Association of Fire Chiefs recommend a carbon monoxide detector on every floor of your home, including the basement. A detector should be located within 10 feet of each bedroom door and there should be one near or over any attached garage. Each detector should be replaced every five to six years.
Additional Resource is the National Fire Protection Association (NFPA) http://www.nfpa.org/public-education