Why Do Smoke Detectors Go Off?

Smoke detectors sound alarms not only to alert you to smoke or fire, but also to signal the need for maintenance or to indicate a malfunction.

Failing Battery

When the smoke alarm battery is low, built-in circuitry sounds an alarm. Resetting the alarm will not stop the beeping. Keep spare batteries on hand and replace them rather than removing them to stop the noise.

Failing Detector

Many smoke detectors sound an alarm if critical parts of the circuit malfunction. In this case the battery would check out fine, there would be no fire in the building, but resetting the detector would not stop the alarm. Consult the manufacturer's instructions to interpret the signal given by the detector. The pattern of beeps for a circuit malfunction differs from the signal for fire or low battery. Many smoke detector makers replace defective units free of charge within the limits of the warranty.

Combustion Gases

Smoke detectors come in two basic types--particle detectors and ionization detectors.

Ionization detectors use a small chamber irradiated by a small amount of americium to detect combustion byproducts in the air. The americium radiation ionizes air molecules in the chamber, creating a small electric current. Combustion gases include invisible particles that disrupt the electrical connection and trigger the alarm.

Ionization detectors respond to fires that produce very little soot and smoke. According to the National Bureau of Standards, ionization detectors respond faster to flaming fires, while particle detectors react more quickly to smoldering fires.

Smoke

Particle detectors sound an alarm when a photoelectric receptor detects light bouncing off nearby particles of smoke. Photoelectric detectors trigger fewer false alarms from steam or cooking fumes than do ionization detectors.

Both types of detectors should be included in a home fire alarm network. If alarms sound frequently in response to steam or heat--for example, in the kitchen--place the detector elsewhere in the home. If the detector can't be moved, open a window when cooking or showering. Clean the smoke alarm cover and remove any dead bugs or other debris. Always replace the alarm cover after changing the battery.

Maintenance

Test all smoke detectors manually every month. For a better appraisal of its effectiveness blow some smoke directly into the device. Clean the smoke alarm cover and remove any dead bugs or other debris. Replace smoke alarm batteries annually whether the low battery alarm sounds or not. Always replace the alarm cover after changing the battery.

Most detectors have an expected lifetime of less than 10 years--do not buy secondhand devices, which may be near the end of that cycle. The National Fire Protection Association reports that the death rate from house fires in homes without smoke alarms is twice as high as for those with working smoke detectors.

References

• Home Smoke Detectors
• Smoke Alarms in U.S. Home Fires
• Adding Smoke Detection to Home Security Systems

Resources

• Smoke Detector Maintenance Tips