Smoke Alarms 101

The Basics

Smoke alarms should be placed, at a minimum, on every floor level including the basement, inside every sleeping room, and outside of every sleeping area of all dwellings.

Interconnected smoke alarms, either wired or wireless, should be strongly considered. With interconnected alarms, when one smoke alarm sounds, all other smoke alarms in the home sound as well, which creates an early warning to occupants in all areas and allows as much time as possible to escape.


The Details

Sensor Types

There are three types of sensor technology used in smoke alarms: photoelectric, ionization and a combination or dual sensor that incorporates both sensors in one smoke alarm.

  • Photoelectric: The sensor of choice. The photoelectric sensor responds faster (sometimes tens of minutes faster than the ionization sensor) to the smoldering stage of a fire that causes the most injuries and deaths in residences. It is also effective in all other fire stages. It is also less prone to nuisance false alarms from cooking and steam.
  • Ionization: The ionization sensor responds faster (sometimes seconds faster than the photoelectric sensor) to the flaming stage of a fire. It is not effective in the other fire stages. It is more prone to nuisance false alarms from cooking and steam.
  • Combination or Dual Sensor: Contains a photoelectric and ionization sensor. It is still more prone to false alarms from cooking and steam due to the ionization sensor component.
  • Smoke alarms should bear the label of an approved testing agency (UL or FM).
  • To aid in choosing the correct smoke alarm, look for the letter “P” or the word “photoelectric” on the packaging or description of the smoke alarm.

Power Types

  • Battery: Uses 9 volt or AA batteries
  • Long Life Battery: Power may last up to 10 years with a long-life lithium battery.
  • Hardwired: Wired to the home 110 volt electrical service (with battery back-up)
    Battery smoke alarms are readily available and can be installed by a homeowner or tenant. Hardwired alarms must be installed by a qualified electrician but can be easily replaced by the homeowner at the end of their service life or if faulty.


  • Photoelectric smoke alarms should be placed, at a minimum, on every level of the home including the basement, outside every sleeping area and in every bedroom. On all floors, a smoke alarm should be placed at the base of the stairs to the floor above. Smoke alarms should be mounted on the ceiling or high on the wall (smoke rises). Always follow the manufacturer’s instructions.
  • Additional smoke alarms can be added to increase your protection.

Testing and Maintenance

  • Test each smoke alarm monthly by pushing the button.
  • Replace 9 volt and AA batteries in smoke alarms twice a year.  (Remember: change your clocks, change your batteries.)
  • If the alarm “chirps,” warning that the battery is low, replace the battery right away.
  • All smoke alarms have a recommended service life of 10 years. Replace your smoke alarms at this time or sooner if they are not functioning properly.
  • Vacuum or dust out cobwebs and dust that have accumulated in smoke alarms at least once per year.

Additional Tips

  • Consider installing interconnected smoke alarms (wired or wireless). When one smoke alarm sounds, every alarm throughout the house sounds. Here's some more information about Wireless Interconnected Smoke Alarms
  • In the event of a false alarm, never remove the battery or disconnect the power source. Simply fan the smoke or steam away from the smoke alarm until the alarm stops. Some smoke alarms come with a button you can push to temporarily silence the alarm.
  • If a contractor or supplier is installing your smoke alarm, make sure you are provided with the manufacturer’s instructions.
  • Many communities provide free smoke alarms and batteries to residents who cannot afford them, and may install them for you if you require assistance. Check with your local fire department.
  • Smoke alarms are one component of a complete home fire escape plan. Have a plan and practice it.