How (and Where) to Install Smoke and Carbon Monoxide Detectors

Man installing smoke or carbon monoxide detector.
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Smoke and carbon monoxide detectors offer inexpensive protection and are easy to install.

Almost two thirds of deaths in home fires occur in homes without smoke detectors or with smoke detectors that are not working. Having enough working detectors and mounting them properly in your home provides inexpensive peace of mind.

Carbon monoxide (CO) is a colorless, odorless and lethal gas, sometimes produced by faulty furnaces, water heaters and gas dryers. Since it's otherwise undetectable, it's essential to have a carbon monoxide detector on every floor of your home, even the basement.

As important as having smoke and CO detectors in the right quantity and choosing the best ones you can afford is knowing where to locate them and which kinds of sensors work best in those locations. There are two basic types of smoke detector sensors: ionization and photoelectric. Each sensor type excels in different circumstances and each has advantages to consider.

Ionization Versus Photoelectric Detectors

Ionization smoke detectors employ an ionization chamber containing a small amount of a radioactive element, americum-241. A small electric current is passed between two metal plates in the ionization chamber. When smoke enters the chamber, it disrupts the current and an alarm is triggered. Ionization smoke detectors tend to be the least expensive ones and are therefore the most common ones found in homes. They aren't always the best choice, however. While ionization alarms have a slight advantage over photoelectric ones in detecting hot, fast-burning fires, they are also prone to false alarms from cooking smoke or even shower steam. After a few of these incidents of nuisance tripping, homeowners often disable the unit.

Photoelectric smoke detectors surpass ionization ones when the fire is slower and smoldering. They may be a better choice, because smoke inhalation is more often the cause of fatality than is the fire itself. Photoelectric sensors use a beam of light and a light-sensitive electric sensor, positioned so that under ordinary circumstances the light beam passes the face of the sensor without registering. When smoke enters the beam, however, it scatters the light, causing enough of it to strike the sensor that the alarm is triggered. Photoelectric alarms are less prone to nuisance tripping than are ionization alarms, and they are the only sensor type recommended by the International Association of Fire Fighters.

Some smoke detectors are available are dual alarms, containing both ionization and photoelectric sensors. While once popular, these dual sensor alarms are no longer favored and authorities instead advise a combination of both types of single-sensor detectors.

Alarm Maintenance

It's a good idea to replace the batteries in your smoke alarms twice a year. Some newer alarms come with a ten-year lithium battery that never needs replacing—after ten years you replace the whole unit. Fire prevention authorities recommend replacing all your smoke alarms every ten years anyway. In the year 2000, smoke alarm manufacturers began including the date of manufacture on the back of their alarms, so it's easy to determine their age. Carbon monoxide monitors also have a limited life. Check their date of manufacture and replace them as the manufacturer advises. Lightly vacuum alarms if dust accumulates, and never paint any part of your alarms.

Alarm Placement

You should have a smoke alarm on each floor of your home and one in each bedroom, plus one in the basement near the stairway. Alarms should be at least twenty feet from smoke and combustion particle-producing features such as fireplaces, stoves, and furnaces. Avoid high humidity areas such as showers and laundry rooms. Fans and ventilation ducts can keep smoke from reaching the sensor, so locate your smoke alarms away from areas of active air flow.

Because smoke rises, smoke alarms should be mounted on the ceiling or high on the wall. If on the ceiling, the unit should be no closer than four inches from the wall. If on the wall, the unit should be no closer than four inches from the ceiling and no more than twelve inches below it.

Carbon monoxide detectors should not be mounted on the ceiling but can be placed at any level on the wall because CO does not rise. You should have a carbon monoxide detector on each floor. Combined smoke and carbon monoxide detectors are also available. If you choose one of those, mount it on the wall within twelve inches of the ceiling.

How to Mount a Smoke or CO Detector

Things You'll Need

  • Smoke detector or CO detector

  • Correct batteries

  • Stepladder

  • Pencil

  • Tape measure

  • Drill

  • Drill bits

  • Hammer

  • Screwdriver

  1. Determine the location where you will install the smoke alarm. With the template (if included) or using the mounting bracket as a template, mark where you will drill.
  2. Select a drill bit slightly smaller than the diameter of the plastic anchors supplied with the smoke alarm. Drill the holes and insert the screw anchors. With the hammer, tap the anchors flush with the surface.
  3. With a drill driver or screwdriver and screws, attach the mounting bracket.
  4. Insert batteries into the unit. Test, using the test button. Mount the smoke detector to the bracket by fitting it into the interlocking slots and twisting the unit slightly until it locks in place. Some CO detectors slide into place.
  5. Test the smoke alarm again.

Networked Alarms

A new generation of smoke detectors is designed so they can "talk" to each other. These wirelessly connected units will all sound an alarm when any one of them detects smoke. In addition, some of these networked alarms will also indicate which of the units has detected smoke. The network that wirelessly connects them is self-contained and independent of cellular signals or a wireless internet system. Also available are smoke detector and carbon monoxide detectors you can access and monitor through an app via smart phone.

Explore the alternatives, read the reviews and make your choice. You're sure to find smoke detectors and carbon monoxide detectors that suit your preferences and fit your budget. No matter which detectors you choose, your home will be vastly safer with them than without them.


Bill Nelson

Bill Nelson

A former agency art director then freelance designer, illustrator and copywriter, Bill has written for the medical, technical, industrial, food and agricultural industries. With over 35 years experience in the area of home improvement. He has produced books on multiple subjects for Home Depot, The Handyman Club of America, Hometime, Black & Decker and Popular Mechanics.