QDEAR BARRY: We are remodeling our home and would like to upgrade the smoke alarm system to comply with current safety standards. This may not be required for an older home, but we would like to do it anyway. We also want to install carbon monoxide detectors. What can you tell us regarding these upgrades? -- Raymond

ADEAR RAYMOND: Retrofitting a modern smoke alarm system in an older home can become quite involved, because standards require the interconnection of all alarms. This means that a network of wires will be needed, allowing each smoke alarm to activate the other alarms in your home.

Required locations for smoke detectors in a single-family dwelling include one in each bedroom, one outside each separate sleeping area, and at least one on each additional story of the dwelling, including basements and cellars. In most locales, alarms are not required in subareas and attics.

The power source for smoke alarms should include direct wiring to the primary electrical system, plus battery backup in case of a power failure during a fire.

Although they are not yet a requirement in most municipalities, carbon monoxide detectors are highly recommended to prevent asphyxiation by faulty fuel-burning appliances. Some manufacturers of smoke detectors produce combination fixtures that react to smoke or carbon monoxide. But smoke detectors work best near ceilings, because smoke rises, while carbon monoxide detectors are best when located near the floor, because carbon monoxide is heavier than air. Therefore, separate fixtures are a good idea. You can buy carbon monoxide alarms that plug into standard wall outlets, typically located within a foot of the floor.

To ensure proper installation of your smoke alarm system, have the wiring installed by a licensed electrician. Be sure to consult your local building department regarding specific requirement that may differ from the general standards listed here.

DEAR BARRY: In the middle of the night, my hard-wired smoke detector went off, sounding for about a minute, waking everyone in the house, and finally shutting off. In the morning, this happened two more times. What could be causing this malfunction? Is the detector simply old and in need of replacement? What do you recommend? -- Herbert

DEAR HERBERT: If your smoke detector is hard-wired, without battery backup, then we can rule out the possibility of a battery in need of replacement. As you suggest, the problem could be that the fixture is old and should be replaced. However, it is also possible that there is a small creature living in the device, such as a spider. This is a common cause of false alarms.

Every smoke alarm contains a small chamber in which a stream of radioactive particles is projected against a specialized receptor. If any objects interrupt this transmission, such as smoke molecules or a spider, the alarm is activated. No matter the cause, you should replace the device.

Barry Stone is a professional home inspector. If you have questions or comments, contact him through his Web site, www.housedetective.com, or send mail to 1776 Jami Lee Ct., Suite 218, San Luis Obispo, Calif. 93401.

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