Kentucky Injury Prevention and Research Center

Smoke Alarms


One of the easiest and most effective ways to protect yourself and your family from fire is to install smoke alarms in your home.  Unfortunately, many people don’t take advantage of the protection that smoke alarms provide.  This page will provide you with information that can help you select, install and maintain smoke alarms.


The Benefits of Smoke Alarms


Approximately 13 out of 14 homes in the US now have smoke alarms installed.  Almost half of all home fires, however, occur in homes without working smoke alarms.  Over sixty percent of fire deaths occur in homes without working smoke alarms.  Obviously, most of the people who are killed by residential fires die in a small percentage of homes - those without smoke alarms.


Smoke alarms can warn you of a fire when you are asleep, busy or in a different part of the house from where the fire is.  They provide you extra warning time when you are awake, and they will wake you if a fire occurs while you are asleep.  Many people think that they will smell smoke and wake up if a fire occurs in their home, but this isn’t true.  Many fires produce odorless gasses that are very toxic.  People who are asleep can be overcome by these gasses without ever waking up.  Smoke alarms provide life-saving warnings to allow you to get out of the house before you are trapped by fire or smoke.


Smoke alarms are inexpensive.  Battery-operated residential smoke alarms are available for less than $10.  Alkaline batteries that can last for a year are available for $1 to $2 each.  Some alarms are now available with long-life lithium batteries.  These alarms, which typically sell for about $20, have lithium batteries that can last for up to ten years.


How Smoke Alarms Work


Smoke alarms, which are also called smoke detectors, work by constantly checking the air for traces of the gasses and smoke particles produced by a fire.  There are two types of smoke alarms - ionization alarms and photoelectric alarms.  Ionization alarms are less expensive, and they detect fast, flaming fires more readily.  Photoelectric alarms are a bit more expensive, and they detect slow, smoldering fires better.  Photoelectric alarms are also less sensitive to steam from showers and cooking food so they are the best choice for alarms that will be installed near kitchens or bathrooms.  You can learn more about smoke alarms by reading the Smoke Alarm Installation Manual on this web site.


Some smoke alarms are powered by the normal household wiring.  This type of smoke alarm should have a battery for back-up power, since fires can occur when the normal electrical power is not working.  Other smoke alarms are powered by batteries.  Regardless of the type of alarm you have, it is important that you maintain it properly. 


Installing Smoke Alarms


One smoke alarm is not enough for most homes.  The National Fire Protection Association recommends that each floor of a home should have at least one alarm, and that there should be one alarm outside of each sleeping area in the house.  For example, suppose that you have a two-story house with a basement.  You will need at least three alarms - one in the basement, one on the first floor and one on the second floor.  If there are bedrooms in separate areas of the same floor - such as a master bedroom at the east end of the house and children’s rooms at the west end - then an alarm should be installed in each sleeping area.  That means that you might need two, or even three, alarms on one floor if people sleep in different areas of the house.  (Don’t forget to include other areas where people sleep.  If you sometimes sleep on the couch in your living room or den, that room is a sleeping area.)


The best place for a smoke alarm is on the ceiling, at least 4 inches from the nearest wall.  If the ceiling has a high point, such as a gabled or vaulted ceiling, install the alarm at or near the highest point of the ceiling.  Since the hot gasses and smoke produced by fires rise, you want to install the alarm at the point where those gasses will collect first.


You can also install alarms on walls.  Alarms installed on a wall should be at least 4 inches below the ceiling, but not more than 12 inches below the ceiling.  Try to avoid installing alarms in areas that regularly become very hot or very cold.   Don’t install alarms near windows, doors or fireplaces, since drafts could pull smoke away from the alarm and keep it from sounding if a fire occurs.


In general, it’s best to avoid installing ionization alarms in the kitchen or bathroom, or any other place where steam is common.  If you need a smoke alarm in these locations, consider using a photoelectric alarm.  This will reduce false alarms (also called “nuisance alarms”) caused by steam.  You should normally also not install smoke alarms in garages, attics or other similar areas.  Read the instructions provided by the smoke alarm manufacturer for installation instructions for your smoke alarms.


Maintenance is the Key to Safety


Many people have smoke alarms that don’t work.  This isn’t because the alarms were defective, but because they were not properly cared for.  Like any other piece of electronic equipment, smoke alarms must be maintained properly.  Having a smoke alarm that doesn’t work can be a fatal mistake.  Take care of your smoke alarms and they will take care of you.


The first requirement for smoke alarm care is proper feeding - a smoke alarm will not work if the battery that powers it is dead.  You should follow the manufacturer’s directions for changing the batteries in your smoke alarms.  If you have a lithium powered 10-year alarm you may need to change the battery only if the alarm fails a test.  For most smoke alarms, however, you should change the battery at least once per year.  Many people change the battery twice per year, when they change their clocks to and from Daylight Savings Time in the spring and fall.   Use good quality alkaline batteries in your smoke alarms, and test all alarms after a new battery has been installed.  Most current smoke alarms have low-battery alarms that “chirp” or beep when the alarm battery is low.  If the low battery alert sounds, change the battery in the smoke alarm immediately.


Testing a smoke alarm is very important.  Smoke alarms are delicate electronic devices that operate around the clock, year after year.  Sooner or later, some of them break down.  The only way to know if a smoke alarm is still working is to test it.  To test a smoke alarm, follow these steps:

  1. Push the test button on the alarm. (If you can’t reach the alarm, use a broomstick to push the button.)
  2. If the alarm sounds, the alarm is OK.
  3. If the alarm does not sound, replace the battery and push the test button again.
  4. If the alarm still does not work after the battery is replaced, the alarm is defective. Replace it immediately.

You should test the smoke alarms in your home at least once per month, or more often if the manufacturer’s directions recommend it.


Cleaning your smoke alarms is also important.  If the alarm vents or sensor become clogged with dirt and dust the alarm will not work.  You should follow the manufacturer’s directions for cleaning each alarm.  In most cases you can use a vacuum cleaner to remove dirt and dust.  If you will be doing work near a smoke alarm that will produce a lot of dust, such as sanding or installing drywall, cover the alarm with a plastic bag.  Remove the bag as soon as you are finished with the work.  Never paint a smoke alarm - the paint can clog the vents.


Replace a smoke alarm if it fails a test (see above).  You should also replace alarms whenever they become ten years old.  Like any other electronic device, smoke alarms can fail, and the chance that an alarm will fail increases as the alarm becomes older.  There is about a 30 percent chance of alarm failure by the time an alarm is ten years old.  Older alarms have even higher chances of failing.


Nuisance Alarms


Sometimes smoke alarms will sound when there is no fire.  In many cases, this happens when a controlled fire (such as a candle or a fuel-burning heater) releases smoke and gasses into the air.  Steam from cooking or bathing can also cause some smoke alarms to sound.  In these cases, you can push the silence button (sometimes called a “hush button”) on the alarm to silence it for a few minutes, then air out the house to remove the smoke or steam.  This should fix the problem.


A nuisance alarm can also occur with no fire at all present.  In these cases, the smoke alarm may need cleaning.  Try cleaning the alarm and replacing the battery with a new one.  If this doesn’t work, you may need to replace the smoke alarm.




Smoke alarms save lives.  If your home has smoke alarms, check them to be sure that they are clean, test them and install new batteries when needed.  If your home doesn’t have smoke alarms, invest the few dollars needed to purchase and install them.  Your life is worth it.


For additional information about smoke alarms, check out some of the links on the Fire Safety page.