The Function of a Smoke Detector

Smoke detectors are important home safety tools because they increase your chance of escaping from a house fire. Properly functioning detectors give you an early warning that makes escape more likely, but the unit is more than just an alarm. Understanding the primary functions of a smoke detector makes it clear to see why you need them properly installed an working well.

Smoke/Carbon Monoxide Detector
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The Function of a Smoke Detector

Parts of a Smoke Detector

Smoke detectors have two main components: the sensor and the alarm. Both components play an important role in the overall purpose of the unit, which is to sense fires as soon as possible and alert anyone in the home, so they can get out. These components are equally important. Sensing the fire does no good if the alarm isn't loud and functioning. A poor sensor fails to send out the alert soon enough to get people out of the home.

Detection of Smoke and Fires

A smoke detector's initial function is detecting that fire is present. The way it senses the fire depends on the type of detector it is. A photoelectric model has a light source that goes into the sensing chamber. The light sits at an angle away from the sensor. When smoke enters, it causes the light to reflect onto the sensor, triggering the alarm. These units are best at detecting smoldering fires that start with smoke before eventually breaking into flames.

An ionization model uses radioactive material positioned between two electrically charged plates to ionize the air inside of it. This creates a current flow between the two plates. Smoke sets off the alarm when it disrupts the ion flow. These detectors are most responsive to fires with blazing flames.

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. Because each type is ideal for a certain type of fire, it's a good idea to have at least one of each in your home. You can also get a combination model that uses both photoelectric and ionization methods for detecting smoke.

Warning Home Occupants

Once a smoke detector senses smoke, its next job is to let people know about it. That warning can make the difference in whether or not people in the home have time to escape. Effective detectors should have alarms of at least 85 decibels at 10 feet, so they can be heard throughout the home. Smoke detectors are often located outside of bedroom doors. That means the alert sound needs to be loud enough to go through doors and wake up sleeping people in case of a fire at night. Detectors should also have a low-battery notification function that makes a repetitive beep when the battery power is nearly drained.

Testing the Functions of the Detector

Smoke detectors do not last forever. It's a good idea to replace your smoke detectors every 10 years to make sure you have reliable detection of fires. 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. Older units may sound when you press the test button, but that doesn't tell you how well the sensor works. The test response simply tells you that the electronic components and alert part of the detector still work. You can test the sensor by using smoke alarm test spray, but it's still a good idea to change out any units older than 10 years. The sensor could stop working at any time. Not sure how old your unit is? Look on the back side for a date. That's the manufacture date, and it's what you should use to calculate the 10-year mark, even if you installed it much later.