Smoke Alarms Save Lives!

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Smoke Detector Graphic 2 

Questions and Answers

What is a smoke alarm?

A smoke alarm is a battery-operated or electrically-connected device that senses the presence of visible or invisible particles produced by combustion and that is designed to sound an alarm within the room or suite within which it is located.

Are smoke alarms effective?

The largest percentage of fire deaths in the home occurs at night while people are asleep. Therefore, a working smoke alarm can provide an early warning that can make the difference between life and death. According to studies published by the National Fire Protection Association, having a smoke detector cuts your risk of dying in a fire by nearly half. However, a smoke alarm should be part of an overall home fire safety strategy that also includes preventing fires by adopting fire-safe behavior and developing and practicing a home fire escape plan. In a fire, escape time may be very limited. Therefore, escape plans are a critical aspect of a home fire safety strategy. For additional information on the effectiveness of smoke alarms, refer to the Smoke Alarm Fact sheet.

What is the principal reason for smoke alarms not functioning?

Over a recent three-year period, an analysis was undertaken of people who died in homes where smoke alarms were present but did not work. 85% of those victims did not have a functioning smoke alarm because of a dead or missing battery/power source.

What types of smoke alarms are available on the market?

There are two types of household smoke alarms in common use. These are known as ionization or photoelectric smoke alarms.

How does an ionization smoke alarm work?

This type of alarm uses a small amount of radioactive material to ionize air in the sensing chamber. As a result, the air chamber becomes conductive, permitting current to flow between two charged electrodes. When smoke particles enter the chamber, the conductivity of the chamber air decreases. When this reduction in conductivity is reduced to a predetermined level, the alarm is set off. Most smoke alarms in use are of this type.

How does a photoelectric smoke alarm work?

A photoelectric smoke alarm consists of a light-emitting diode and a light-sensitive sensor in the sensing chamber. The presence of suspended smoke particles in the chamber scatters the light beam. This scattered light is detected and sets off the alarm.

Which type of alarm is more effective?

There is no simple answer to this question. The two types operate on different principles and, therefore, may respond differently to various conditions. Some advantages to each type are set out below:


  • Fastest type to respond to flaming fires.
  • Lowest cost and most commonly sold.
  • Some models have a hush or temporary silence feature that allows silencing without removing the battery.
  • Some models are available with a long-life battery.


  • Fastest type to respond to slow smoldering fires and white or gray smoke.
  • Less prone to nuisance alarms from cooking.

Notwithstanding these differences, to achieve UL listing, both alarms must be tested to the same standard and meet the same requirements. Photoelectric smoke alarms may respond slightly faster to smoldering fires, while ionization alarms respond slightly faster to flaming fires. Since you can't predict the type of fire that will occur, it is difficult to recommend which is best. Both alarms will detect all types of fires that commonly occur in the home. Installing both types of smoke alarms in your home can enhance fire safety.

California Fire Code on Smoke Detectors:  [Click Here]