How Does a Smoke Detector Work?

Smoke detectors are essential for keeping your home and your family safe. But few of us actually know how these devices work. We’ll go over everything you need to know in this article, including how to choose the right smoke detector for your home.

First, let’s talk about what’s actually going on inside these devices that allows them to detect smoke in the air.

There are two basic types of technology that smoke alarms use: ionization and photoelectric. How your smoke detector works depends on which technology it uses (some of the best smoke detectors use both). Here’s a breakdown of how these two technologies work, starting with ionization.

Ionization smoke detectors use a tiny amount of radioactive material to function. Yes, we said radioactive material, but don’t worry, it’s a very miniscule amount and is protected by a shield, so you won’t end up irradiated.

This radioactive material is placed between two metal plates, charging the air there with electricity. When smoke enters the electrically charged air between the plates, it disrupts the current and sets the alarm off.

Photoelectric smoke detectors use a light source that is shined through a small chamber. There is also a light sensor in the chamber, but the light is situated so that it doesn't shine into the sensor. When smoke enters the chamber, it reflects the light, which in turn sets off the sensor.

Smart smoke detectors are devices that can pair with a smart home hub and other devices to send you alerts, help you monitor your home when you’re away, and tell you when to change its batteries.

Smart smoke detectors use the same technology as normal smoke alarms to actually detect fires/smoke in your home. The difference is in the other technologies (like Wi-Fi, Bluetooth, and Matter) that they use to communicate with your whole smart home ecosystem.

We’ve all been woken up by a false alarm. While we know deep down that we should be thankful that we have functional smoke detectors in our house, our first impulse is probably to smash the thing that’s making that dreadful noise with a hammer.

So, why do your smoke alarms go off when there’s not actually a fire (or even smoke) in your house?

Sometimes a false alarm is obvious to diagnose. If you’ve been cooking rice and you left it on the burner too long, your alarm is probably just detecting the very real smoke in the air.

But there are times when your smoke alarm can go off for no apparent reason. Here are the most common factors that may be coming into play:

• Humidity: If it’s the middle of July and there’s 90% humidity in the air, your smoke alarms may start acting funky. The same thing can happen if your detector is set up close to a steaming shower. Water vapor acts similarly to smoke, so it can trigger a false alarm, especially in ionization-style smoke alarms.
• Low batteries: Many smoke alarms will beep when they are low on batteries. While this isn’t a false alarm, it can be annoying. But smoke alarms work less well in general when they are low on batteries, making it more likely that you will end up with a false alarm.
• Volatile organic compounds: if you’re repainting your room, using strong cleaning products, or doing some DIY chemistry in your home, you may trigger your smoke alarm. That’s because some of the chemicals in these substances can confuse your smoke detectors.
• Bad placement: If your alarms are in places with a lot of ventilation or air movement—like by a window or a door—then they are more likely to be triggered by fast moving air or outside smoke.
• Insects: I once had a landlord that blamed all of the false alarms in our building on spiders. I thought he was full of it, but it turns out that small insects can get into the holes on your smoke detector and trigger a false alarm.

There are several factors to consider when you’re picking a new smoke detector.

While most devices look basically the same, there can be some significant differences between them.

In general, ionization-style smoke detectors are better at responding to big fires that are actively flaming. Meanwhile, photoelectric-style smoke detectors are more effective for responding to slower-burning or smoldering fires. Both kinds are fine choices for most homes, though getting a smoke detector that uses both technologies is a surefire (no pun intended) way to protect yourself and your home.

You’ll also want to consider whether you want wired smoke detectors or battery powered smoke detectors. Wired alarms are more reliable in general, and they almost always have a backup battery, in case power goes out. They can be connected together, so that if one alarm goes off, it will trigger the alarms in every part of the house. But, battery powered devices are often easier to install.

Finally, you should consider buying a smart smoke detector, like the Google Nest Protect. These devices can wireless connect with your smart speaker, home security system, and other devices. You can monitor your alarm history and see notifications about low batteries or triggered alarms, even when you are away from home.

We actually have a whole article dedicated to reviewing the very best smoke detectors available for every kind of household. But, in general, we recommend going with an established brand like First Alert, Kidde, and Google.

There are times when you might want to take a leap and get some fancy new gadget from a startup company. But this is not that time.