The Function of a Smoke Detector

Smoke detectors are important home safety tools because they increase your chance of escaping from a house fire. Statistics from 2003 to 2006 showed that twice as many fire fatalities happened in homes without smoke detectors than in protected dwellings, according to the National Fire Protection Association. Properly functioning detectors give an early warning that makes escape more likely.

Smoke detectors sound an alarm in the presence of smoke.


A smoke detector's initial function is detecting that fire is present. The two types of detectors each accomplish this through a different method. Photoelectric models have a light source that reacts to smoke by reflecting the light onto a sensor, triggering the alarm. These units are best at detecting smoldering fires that start with smoke before eventually breaking into flames. Ionization models use radioactive material to ionize the air inside of them. Smoke sets off the alarm when it disrupts the ion flow. These detectors are most responsive to fires with blazing flames.


Smoke detectors must issue a warning once they detect a fire so people in the home have time to escape. Effective detectors should have alarms of at least 85 decibels, so they can be heard through doors and wake up sleeping people. Detectors should also have a low-battery notification function that makes a repetitive beep when the battery power is nearly drained.


Smoke detectors do not last forever. Most units have a lifespan of eight to 10 years, according to the U. S. Fire Administration, but it is critical to replace them before they malfunction so you have continuous protection. Most models have a test function that lets you periodically check them to catch potential problems early. Test your smoke detectors monthly and immediately replace any units that do not respond as they should. Get new detectors after a decade even if the old models still seem to be functioning.


Photoelectric and ionization smoke detectors both have certain advantages that make them more effective in specific areas. For example, a photoelectric model quickly detects smoke from smoldering bedding or furniture in a bedroom or living room or family room, while ionization units give fast warning of a blaze triggered by flammables in a utility room or a stove fire in a kitchen. Select the right detector for each area in your home, or buy combination models that use both ionization and photoelectric sensors, the U. S. Fire Administration advises.