Your Smoke Detector May Not Save You

A smoke detector is important when you buy or sell a house.

Smoke detectors are nothing new. They became prevalent in the 1970’s and are now in ~96% of homes. However, in most cases, smoke detectors are an afterthought; something that you place in your house and don’t think about until it starts beeping at you. Not too long ago, I decided I wanted to put a smoke detector up in one of the open rooms in my house. I went online and decided to do some research on smoke detectors to make sure I got the best one for the location. During my search, I looked into how the detectors work, and as I did, I found out something frightening that I had NEVER heard ANYONE say about smoke detectors.

Now before I jump into what I learned, how much do you know about smoke detectors?

General Guidelines

  • How often should you test your smoke detectors? Every month
  • How often should you change your batteries? Every year (not just when it starts beeping)
  • How often should you replace the smoke detector itself? Every ten years

NOTE: The above statements are general guidelines. Always follow the manufacturer’s recommendations for your particular smoke detectors

Did you know all of these? If you did, great! Now, are you actually doing it?

Lesser Known Details

  • How many different smoke detector types are there (Not CO or heat)? Two
  • What are they? Photoelectric and Ionization
  • Do you know what type of sensor you have in your home?
  • Do you know what type of sensor you should be using?

To answer what you should be using, let’s first understand the difference between the two detectors.


Ionization smoke detector diagram. Houston house
Ionization Detector

The first type of detector is an Ionization smoke detector.

It works by using a small amount of radioactive material (Americium-241) to ionize air. This creates an electric current and closes a circuit. The alarm is set off whenever smoke enters the detector and disrupts the current. These are best at detecting fast, flaming fires that typically produce small particles in the smoke. These are also more prone to false alarms, and can be set-off from things like steam from a shower, or burnt food.


The second detector is a Photoelectric smoke detector.Photoelectric smoke detector. Houston House.

It works by shining a small beam of light aimed away from its sensor. Whenever smoke enters the detector, that beam of light is diffracted (redirected light) into the sensor, and triggers the alarm. The photoelectric detector is best for detecting smoky, smoldering fires that may have little, if any, visible flames. These detectors rarely have false alarms, but can be set off by anything that interferes with the beam of light – things like dust build-up.


Why is this important? – Because the wrong type of detector for the type of fire that occurs could mean the difference between life and death.

Tests have shown that ionization detectors will respond about 30 to 90 seconds faster to “fast-flame” fires than photoelectric smoke alarms. However, in smoldering fires, ionization alarms respond an average of 15 to 50 minutes slower than photoelectric alarms! That is not a typing error, the delay is in minutes and not seconds.

Worse yet, some studies have shown that in smoldering fires, ionization detectors will fail to activate up to 20-25% of the time. This is troubling since the majority of residential fire fatalities are due to smoke inhalation, and almost two-thirds of fire fatalities occur at night while we sleep.

Check out the video below from the NBC Today Show to see a demonstration using the two types of smoke detectors.

NBC TODAY Show Rossen Reports  "Some smoke detectors may not go off in time" - 10/03/2012

As of 2012 – Over 90% of US homes have ionization smoke alarms installed, around 5% of have photoelectric alarms installed and the rest have no alarm of any kind. If you are wondering why so many people have ionization detectors – it is the same reason for most things…they are cheaper.

Currently ionization smoke detectors are actually banned in three states: Massachusetts, Iowa and Vermont due to slow response to smoldering fires.

So, which smoke detector should you have? Both.

Either utilize a combination of detectors or us a dual sensor unit. But don’t just take my word for it. Let us see who else is saying this.

Who Recommends This

National Fire Protection Association – “For best protection, it is recommended both (ionization and photoelectric) technologies be used in homes. In addition to individual ionization and photoelectric alarms, combination alarms that include both technologies in a single device are available.”

National Association of State Fire Marshalls – “As you know, because of the differences in how the different smoke alarm sensing technologies react to different types of fires, NASFM’s Smoke Alarms Guidance Document recommends that homes be protected by both ionization and photoelectric sensor technology, either as separate smoke alarm units both installed in a residence, or as dual sensor units.”

United States Fire Administration – “Because both ionization and photoelectric smoke alarms are better at detecting distinctly different yet potentially fatal fires, and because homeowners cannot predict what type of fire might start in a home, the USFA recommends the installation of both ionization and photoelectric or dual sensor alarms.”

Consumer Product Safety Commission – “Because both ionization and photoelectric smoke alarms are better at detecting distinctly different yet potentially fatal fires, and because homeowners cannot predict what type of fire might start in a home, CPSC staff recommends consumers install both ionization and photoelectric type smoke alarms in their home

These as well as many more! Every authority on fire I was able to find recommends this.

It boggles my mind that this information has not been better communicated, considering how critical it is. Additionally, in most cases, smoke detectors are an afterthought. Something that you place in your house and don’t think about until it starts beeping at you. We must not forget that these are a critical component in protecting us and our families. Please take the time to ensure that your smoke detectors are functional and that you have the appropriate detector type in place. If you have any questions, please email me, or leave a comment below.

Final Thoughts

While this blog is primarily real estate related, I will also take moments to address things I find along the way that I think are important to communicate. I gave a presentation on smoke detectors to over 100 scientific professionals working in the petrochemical industry, many of whom hold a PhD in chemical engineering or chemistry. In that presentation I asked the same questions as I did in this blog; only two people knew about the different detectors, and no one knew about the delayed response when using ionization detectors.

Images used from the NFPA website

In Case You Missed It – Check out our last article “Houston House Problems – Stucco Damage”.

Kevin Bazazzadeh

Kevin is the co-owner of Brilliant Day Homes, and primary author of the Brilliant Day Blog. He uses the blog to help educate home owners on the details of real estate to help them make the best decisions with their biggest asset. Kevin grew up around real estate investing and spent summers working on rental properties for his dad, who runs a home renovation company with Kevin's brother. Kevin enjoys spending time with his wife Savannah, and children Isaac and Amelia. He also has a passion for volunteering and usually spends several hours each week doing so.

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