How Do Smoke Alarms Work?

Smoke alarms or detectors sense small particles in the air then set off their alarm. According to the National Fire Protection Association (NFPA), there are two main types of detectors: photoelectric detectors and ionization detectors.

Ionization Detectors utilize an ionization chamber and an extremely tiny amount of radioactive material. In the chamber are two plates with voltage between them. If smoke comes into the chamber, it disrupts the current and triggers the alarm. Generally speaking, these types of alarms are best at detective fast-moving fires.

Photoelectric Detectors use light to detect smoke. It aims a light source into its chamber, so when smoke comes in it reflects the light, triggering the alarm. This type of detector is typically best at alerting smoldering fires.

The NFPA recommends using both types of detectors, either separately or as a dual unit.

What Can Trigger a Smoke Detector? And How Do You Stop It?

Whenever your smoke detector goes off, it’s important that you first make sure there is no fire in your house. Just because you don’t see or smell a fire doesn’t mean that it’s automatically a false fire alarm. It could be a hidden electrical fire.

However, once you determine that there is no fire, the smoke detector could be triggered by other factors. Below are the most common types of triggers and how to stop the false alarm:

Smoke Detector Placement/Air Movement

Smoke detectors are designed to sense smoke. And it doesn’t have to be a ton of smoke to set off a false alarm; even just an odor of something burning can set it off. That's why placement is important.

Detectors should be placed outside every bedroom, on every level of the house, including the basement. Take care not to place too close to a window or ventilated area, as that fresh air can keep the detector from sensing smoke in the home.

If you're like most people, you've had a smoke alarm go off while you're cooking, even if you're not burning anything. Make sure that your smoke detector is at least 10 feet away from a cooking applicance and not in an area where air movement gets trapped easily.

Detectors mounted on the wall should be placed four to 12 inches from the ceiling, and detectors mounted on the ceiling should be placed four inches away from the wall. These placements offer the best access to regular air movement in the house.

Overcooked/Burned Food

Since smoke detectors actually sense more than just smoke, you likely already know that burning food can set them off. According to the National Institute of Standards and Technology (NIST), smoke alarms can detect the particles coming off your food as it cooks.

Steam or High Humidity

Smoke alarms can't usually tell the difference between smoke particles and moisture particles. It's all about the density here, and the density from the moisture in the air can trigger a false alarm. So be sure to not place an alarm too close to a bathroom. where a steam from shower and moisture collect.

High humidity (85% or higher) can also set off a smoke detector due to the dense nature of the particles. Be sure to air out the area around your detector if you’re experiencing extreme humidity.

Pesky Insects

Yes, those pesky pests could be a reason your smoke detector is chirping. It’s possible that they crawled into the smoke detector and triggered a sensor. You’ll need to remove the smoke detector cover and clean out the device.

Buildup of Dust

Photoelectric smoke detectors can mistake dust in or around the device as smoke because dust particles, like smoke particles, can reflect light. This can easily be fixed by cleaning the device and then resetting it.

Strong Chemicals Nearby

Cleaning agents and paint fumes, especially oil-based paints, can set off a smoke detector. Just like with smoke and steam, you’ll need to air out the area and reset the device.

Batteries Need to be Changed

With a low battery, your smoke detector should be making a different sound, such as short chirps instead of the regular alarm. Check the device manual before installing new batteries.

Smoke Detector Malfunction/End of Life

And if you’re not experiencing any of the above scenarios, your smoke detector may be malfunctioning or has reached the end of its life cycle. A typical lifespan of a smoke detector is around 10 years and after that, you’ll need to replace it. Consult your device manual or local electrician to determine if it’s a malfunction or if the device is dead.

Power Issues

When fire alarms are hard wired, typically they have a backup battery. When the power to the house goes out then turns back on, the alarm may chirp to let you know it's using the backup batter. Read your alarm's user manual to reset and get it back onto hard wire mode. A power outage/spike may also cause your detector to set off a falsa alarm, so simply reset it.

Ripple Frequency

This is also power related, and it will depend your power company. In some areas, electric companies send ripples/signals in the early morning hours to better control things like street lights. This can cause a false alarm on your smoke detector.

Shared Circuits

For hard wired smoke detectors, sharing a circuit with other items in the house can sometimes cause false alarms. That said, experts recommend NOT having smoke alarms on their own circuit. They should share the same circuit as the lighting, especially in an area like the living room. That way, if something goes wrong with the circuit, the lights won't work and the homeowner can fix the issue.

If smoke detectors are on their own circuit and the breaker is tripped or something goes wrong with the circuit, the homeowner won't realize it because the detectors will be off. The number one thing to make sure of is that detectors are installed properly, and that should lessen the number of false alarms.

What If Your Smoke Detector Continues to Go Off?

If the above tips and tricks haven’t solved your smoke alarm woes, you may need to move the smoke detector to another area in your house.

When looking for another area to install your smoke detector, make sure to do it in a climate controlled area and near the bedrooms of the house. Additionally, you should avoid placing smoke detectors near cooking appliances, windows or doors, as they can be affected by drafts, cooking smoke or steam. You should also avoid placing the device in dusty or dirty areas of your house.

As for installing locations, if you install the device on a ceiling, be sure to mount it no closer than four inches to any wall. If you plan to mount it on a wall, place the smoke detector no more than 12 inches from the ceiling. When you measure, use the outside edge of the smoke detector. These placements are optimal for performance and overall home safety.

Adjusting Your Smoke Detector

If your smoke detector keeps going off, it's worth your time to go back to the beginning and re-check that it is installed correctly. Get the user manual (many are available online if you can't find your paper copy) and go through each step to ensure that everything is followed exactly. Make adjustments as necessary. Hopefully, this will help lessen false alarms.

Finding the Right Smoke Detector

Since you can't predict the type of fire you may experience in your home, your best bet is to plan for everything. As explained above, there are two types of smoke detectors: photoelectric detectors and ionization detectors.

Each of them uses different technology to sense a threat. As such, the photoelectric detector is best for alerting when there is a smoldering fire, and the ionization detector is best at alerting when there is a fast-moving fire.

The NFPA recommends using both types of detectors, either separately or as a dual unit. That way, you're covered for every type of fire.

How to Test Your Smoke Detector's Sensitivity

The NFPA suggests having inspection, testing, and maintainance done on your detector regularly. The homeowner or renter occupying the space is responsible for making sure they work. Follow manufacturer guidelines for your detector. You may also contact your local fire department, as many will do testing and even help replace batteries if you need assistance.

How to Adjust Smoke Detector Sensitivity

If you feel comfortable doing so, you can actually ajust the sensitivity of your smoke detector. Using your user manual as a guide, remove your detector's data card, then use a handheld screw driver to adjust the card. Again, read the user manual for advice and to put it back together again.

Additional Smoke Detector Maintenance Tips

What other maintenance tips should you keep in mind when it comes to your smoke detectors? Here are four:

• Keep note of your smoke detector batteries and replace them when their lifespan has ended. Also, keep note of your installation and expiration date of your smoke detectors.

• Clean your smoke detectors every 6 months and use a vacuum extension to suck up the dust.

• Replace your smoke detector every 10 years.

• Test your smoke detectors every couple of months. It may seem excessive, but it can give you a peace of mind knowing that they are functioning properly.

As you can see, when you regularly take care of your smoke detector, the less false alarms you’ll encounter! By taking the time to create a maintenance plan for your smoke detectors, you are making your home a safer place for you and your loved ones.

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