How Do Smoke Detectors Work?

There are two main types of smoke detectors: photoelectric and ionization. Both of these smoke detectors work by constantly running an ongoing, automatic process. These processes are designed so that smoke will interrupt them. When the detector senses that smoke has interrupted their usual process, they sound their alarm.

The difference between photoelectric and ionization detectors is that they both use different processes. As a consequence, not only are both detectors different, but they’re actually good at detecting different kinds of fires. Learning more about the kind of detector you have will help you stay safer in the future. Here’s everything you should know:

How does each smoke detector work?

Photoelectric smoke detectors and ionization smoke detectors use different electric processes to detect smoke. These processes make each better at detecting different types of fire. Here’s why:

1. Photoelectric smoke detectors

Photoelectric smoke detectors contain an LED light that shoots a beam of light across the inside of the smoke detector’s chamber. Beneath this LED light, the chamber also contains a photosensor. Under normal circumstances, the LED light shoots across the chamber without interruption and never touches the photosensor. When smoke enters the chamber, however, smoke particles interrupt the LED beam and scatter its light throughout the chamber. When the scattered light beams hit the photosensor, the alarm activates.

Photoelectric smoke detectors tend to respond notably faster to “smoldering” fires than their ionization counterparts. Smoldering fires usually occur when smoking materials are left unattended. They produce less open flame than “flaming” fires but tend to produce much more smoke. The more smoke a fire produces, the faster the smoke particles will scatter the detector’s LED light and activate the sensor.

2. Ionization smoke detectors

Ionization smoke detectors contain two electrically-charged plates connected to the positive and negative sides of a battery as an incomplete circuit. There is also a radioactive substance called Americium-241 between these plates. Americium-241 continuously “ionizes” air molecules into positive and negative ions. These ions are attracted to the plate with its opposite charge. As ions move toward the plates, they form a “bridge” electricity can pass over to complete the circuit from one plate to the other.

When smoke enters the ionization smoke detector, the ionizes created by Americium-241 bond with smoke molecules. The newly-bonded ions are no longer attracted to the plates, which means the electricity can no longer flow over the ion “bridge” to complete the circuit. When the circuit is broken, the smoke detector activates its alarm. Ionization smoke detectors tend to respond notably faster to “flaming” fires than their photoelectric counterparts. Flaming fires produce more open flame but less heavy smoke than smoldering fires.

Which smoke detector should I use?

One type of smoke detector isn’t “better” than the other. Both ionization and photoelectric detectors will respond to both types of fire; it just so happens each is better at its particular type of fire.

Because you never know which fire your detector will have to respond to, the US Fire Administration recommends all homes use both. You could accomplish this by installing both ionization and photoelectric detectors, or by installing a dual sensor smoke alarm, which contains both types of sensors.

How do I make sure my smoke detector is working?

Warning: Obviously, if your smoke detector is working properly, its alarm will make a very loud noise when you test it.

Your smoke detector should have a “test” button on its face. Press and hold down this button for a few seconds. If it’s working correctly, your detector should sound its very loud, sustained siren for as long as you press the button. If it doesn’t, then your detector’s power source isn’t working. Replace your detector’s battery immediately (most detectors will “chirp” at regular intervals when their battery begins to die). If it uses a power cell or plugs into the wall directly, you’ll have to replace the detector itself.

As an important note: even if your detector is working correctly, you should still maintain it regularly. Replace any batteries it uses at least twice a year. Regardless of detection type or power source, most detectors are rated to last around 10 years. If your detector is any older than that, you should replace it even if it continues working properly.

If replacing your batteries doesn’t solve the problem, then you probably have to replace the smoke detector. You can buy replacement smoke detectors online or in most hardware stores. Just bring your old detector with you so you know what you’ll need to replace it with.

And remember: whether you don’t have a smoke detector, want to install a new one, need help making sure your current detectors work correctly, or just have questions about anything smoke detector-related, Early Bird can always help. We’ll find the right detector for you, put it in, and make sure it’s working quickly, efficiently, and effectively. Guaranteed.