Reuben's Home Inspection Blog


Do You Know What Type of Smoke Alarms You Have? It's Time for an Upgrade.

Do you know what type of smoke alarms you have in your house?   There are two basic types of residential smoke alarms - ionization and photoelectric.  The vast majority of smoke alarms in use today are the ionization type, but they're being questioned more and more as a valid detection method; today they're no longer allowed as the only type of residential smoke alarms in IowaVermont,  and Massachusetts.

Why all the bad press about ionization smoke alarms?

One of the major problems with ionization smoke alarms is that they give off too many false alarms - mostly from cooking and showers.  When a smoke alarm goes off every time someone cooks bacon, people remove the battery or take down the smoke alarm. Manufacturers require them to be installed away from kitchens and bathrooms, but there is no hard and fast rule for clearance requirements across different manufacturers.  Some cities, such as Minneapolis, have implemented even stricter requirements for ionization smoke alarms; they require smoke alarms that are within 20' of a cooking appliance to either be of the photoelectric type, or to have a hush button.

Recent statistics show that in 24% of home fire deaths, smoke alarms were present but did not sound; in half of those cases, there was a missing or disconnected battery.  This is a common problem that I find all the time while doing Truth-In-Sale of Housing evaluations, and the reason people always give is that the smoke alarm goes off every time they cook or shower.

The other problem with ionization smoke alarms is that they take a long time to respond to a smoldering fire - they're tens of minutes slower than photoelectric alarms (page 17).   Estimates show that at least one third of home fatal fires involve a significant smoldering period (page 14).   This is the major reason that there is such a push to replace ionization smoke alarms with photoelectric smoke alarms.  The diagram and text below comes from a handout published by the CPSC, showing how a photoelectric smoke alarm will give occupants much more time to escape in the event of a smoldering fire.

Smoldering Fire

In the event of a smoldering fire, a photoelectric smoke alarm clearly outperforms the ionization type.  So why do we even have ionization alarms?  The main reason is cost.  Photoelectric smoke alarms typically cost about twice as much as the ionization type.  The other reason is that ionization smoke alarms will outperform photoelectric alarms in the event of a fast moving fire.  The faster reaction time can be measured in tens of seconds, but in the event of a fast moving fire, these are precious seconds.  The diagram below, again from the CPSC, helps to illustrate this.

Fast Moving Fire

Most Smoke Alarms are the Ionization Type

I've been hearing more and more about this push, but after recently listening to an impassioned speech on the benefits of photoelectric smoke alarms over ionization alarms, I started taking an informal inventory of the smoke alarms that are installed in Minnesota homes.  Over the past few weeks, I've taken a close look at every smoke alarm in every house I've inspected to get an idea of what's the most common type used in Minnesota.  Out of the dozens of smoke alarms I've looked at, I found one dual-sensor smoke alarm, which employed both ionization and photoelectric technologies.  The rest of the smoke alarms were the ionization type only.  I didn't come across a single photoelectric unit.

To know the difference between ionization and photoelectric alarms, you need to take the smoke alarm down and look at the back.  Ionization alarms all contain a trace amount of a radioactive material, Americium 241.  They'll all have a warning about this on the back side.  Click on any of the thumbnails below to see a blowup of the text on the back side of a smoke alarm - I marked up the labeling that indicates these are ionization alarms in every photo.

First Alert SA86RAC Back 2 Marked UpFirst Alert SA67D Back 3 Marked UpFirex i4618 Back Marked UpFirex 120-1056C Back Marked upFamily Guard FG888D Back Marked UpBRK Electronics 1839WN Back 2 Marked UpKidde 0914 Back Marked Up

Minnesota Requirements

Minnesota currently has no specific requirements when it comes to ionization vs photoelectric smoke detectors.  Smoke alarms are generally required in bedrooms and in common areas on every level of the home in Minnesota, and they need to be hardwired and interconnected when possible.  You can read the full requirements for smoke alarms in Minnesota here.

My Recommendation

I recommend installing both photoelectric and ionization smoke alarms, or smoke alarms that use both technologies called dual alarms.  Some people argue that these alarms shouldn't be used because there could be more nuisance tripping due to the ionization sensor, which would cause the occupants to disable the smoke alarm.  While this is obviously a possibility, proper placement of smoke alarms and better education about how they operate is the best way to make a home safer.

Reuben Saltzman, Structure Tech Home Inspections


Comment balloon 42 commentsReuben Saltzman • April 10 2012 03:17AM


Two important things about smoke alarms that I put on my reports - location and age.  If they are 10 years old or older they must be replaced.  Read the manufacturer recs!  And if they are too close to the kitchen, good luck!

Of course I put links to my blogs on my reports for my clients.  This would be a good link too!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 6 years ago

I'll be removing old and replacing with new with resident turn overs this summer.  They become discolored with age and become very unattractive.

Posted by Wallace S. Gibson, CPM, LandlordWhisperer (Gibson Management Group, Ltd.) over 6 years ago

Jay - I meant to write a comprehensive blog that covered all applicable smoke alarm safety information today, but the ionization vs photoelectric portion was long enough :).  I plan to link to this in my reports too.

Wallace - a yellow smoke alarm is a dead giveaway that it's time for replacement.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

If they are 10 years old they Must be replaced in RI..all the fire marshalls i have dealt with check the dates in them to be i understand why both should be in a home Reuben...

Posted by Ginny Gorman, Homes for Sale in North Kingstown RI and beyond (RI Real Estate Services ~ 401-529-7849~ RI Waterfront Real Estate) over 6 years ago

Ginny - That's good advice.  I recommend the same thing to my clients.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

I have a link to your TracPipe blog on my reports and my clients consult it!  One said they contacted you.  So links work!  And getting people to check into our websites never hurts!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 6 years ago

Such an inexpensive investment to increase safety.  I'm still amazed at how many rental properties I see, with none.

Good post, thanks for sharing it.

Posted by Anthony Daniels, SF Bay Area REO Specialist (Coldwell Banker) over 6 years ago

Actually I didn't before NOW I do, thanks to you!

Posted by Cheryl Thomson REALTOR Army Ret, Associate Broker in Northern Virginia ( United Real Estate (703.216.5635) over 6 years ago

In Frankford Township, NJ, the township requires a smoke/CO2 detector and fire extinguisher inspection prior to closing. It's an excellent requirement.

Posted by Marge over 6 years ago

Well, that would explain the daily sounding of our fire alarm after my fiance exits the bathroom after his shower - ionization! Off to replace the now-disabled-out-of-frustration alarm with a photoelectric version. Thank you for sharing this!

Posted by Mary Elizabeth Allen over 6 years ago

I once had an alarm that would not stop chirping. I did everything you were supposed to do. It imitated a bird call but in the middle of the night, it became a nuisance. I had to call the manufacturer in another state and got a hold of the inventor who walked me through a procedure that corrected it. My thoughts: Either do your job or get out of the house

Posted by Richie Alan Naggar, agent & author (people first...then business Ran Right Realty ) over 6 years ago

Jay - thanks!  I probably include at least a dozen or so links to my web site in every inspection report.

Anthony - me too.  What also amazes me is how people will remove them on purpose because they won't take the time to replace the battery.

Cheryl - until I started researching this topic, I didn't either :)

Marge - I agree.

Mary - hopefully you won't have any more problems with that.

Richie - totally agree.  I once had a similar issue - one of my alarms would chirp in the middle of the night, but it took me forever to figure out which one it was.  Very frustrating.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Reuben, now I know why the smoke alram right outside of our kitchen goes off every time we open the oven door. Thanks for the info.

Posted by Michael Setunsky, Your Commercial Real Estate Link to Northern VA over 6 years ago

Excellent information, Rueben.  The graphs were great.  I can use this with my real estate business and my contracting business!  Good job.

Posted by Mike Cooper, Your Winchester, VA Real Estate Sales Pro (Cornerstone Business Group Inc) over 6 years ago

Funny to see this as the fire trucks are out behind my property putting out a brush fire.

Posted by Cindy Jones, Pentagon, Fort Belvoir & Quantico Real Estate News (Integrity Real Estate Group) over 6 years ago

Very interesting! I didn't even know there were 2 types of smoke alarms. I'm going to look into this!

Posted by Sylvie Stuart, Home Buying, Home Selling and Investment - Flagsta (Realty One Group Mountain Desert 928-600-2765) over 6 years ago

GREAT INFO!! I'll have to check out my OWN detectors now!

Posted by Travis "the SOLD man" Parker; Associate Broker, email: / cell: 334-494-7846 (Team Linda Simmons, Enterprise, AL 36330) over 6 years ago

Reuben, Spot on blog. I have a link in my reports on both type of smoke alarms. Giving the pluses and minuses and recommend both types (as well as replacement in 10 years).

I did not know that some state restricted them which is very interesting. I know that the NFPA recommends both as suitable. 

These are the simplest insurance policy a person can get.

They also make units specifically for areas like kitchens.

Posted by Donald Hester, NCW Home Inspections, LLC (NCW Home Inspections, LLC) over 6 years ago
Lot's of good info here. Thanks
Posted by John DL Arendsen, Crest Backyard Homes "ADU" dealer & Contractor (CREST BACKYARD HOMES, ON THE LEVEL GENERAL & FACTORY BUILT HOME CONTRACTOR, TAG REAL ESTATE SALES & INVESTMENTS) over 6 years ago

I have learned a great deal from this post.  My own smoke alarms are greater than ten years old!

Posted by Sharon Parisi, Dallas Homes (United Real Estate Dallas ) over 6 years ago

I don't know but I better check BEFORE the fire right?

Posted by Lyn Sims, Schaumburg IL Real Estate (RE/MAX Suburban) over 6 years ago

Hi Reuben, great post.  Really liked the graphic.  Are the dual mode much more expensive?

Posted by Bob Miller, The Ocala Dream Team (Keller Williams Cornerstone Realty) over 6 years ago

Reuben, thanks for the tips and reminders, time to do our audit of our rentals again soon, sometimes we get surprises when we check these.

Posted by Bob Crane, Forestland Experts! 715-204-9671 (Woodland Management Service / Woodland Real Estate, Keller Williams fox cities) over 6 years ago

I don't know what type I have, but I do know I hate it when it goes off while cooking dinner.

Posted by Gene Riemenschneider, Turning Houses into Homes (Home Point Real Estate) over 6 years ago

Outstanding post!

Posted by Marshall Brown, BSEE, CHI (Mid America Inspection Services, LLC) over 6 years ago

Another valuable lesson about smoke alarms found in the AR forum. Thanks for a very informative and illustrative post.

Posted by Kimo Jarrett, Pro Lifestyle Solutions (WikiWiki Realty) over 6 years ago

Michael - definitely time for a new type of smoke alarm.

Mike - glad to help spread the information.

Cindy - good timing, huh?

Sylvie - you'll be hearing more and more about this, I'm sure.

Travis - I already know what you have in your house ;)

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Donald - the state restriction is something that has apparently been a big push of the the Duputy Chief of the Boston Fire Dept, Jay Fleming.  He wrote a letter to the CPSC urging them to recommend only photoelectric smoke alarms.  After getting no response, he had Senator John Kerry write them a letter for comment; I guess he has some sway.  He wrote a fairly long comment on this post in our local newspaper where I also publish my blog - .  

John - thanks.

Sharon - just one more excuse to replace them.  

Lyn - let me check for you. ....  You have ionization alarms ;)

Bob - yes, about $8 more.  When you consider the 10-year life expectancy of a smoke alarm, I don't think it makes much of a difference.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Bob Crane - If I had a rental unit, I'd probably only be installing the photoelectric units.  Less nuisance alarms.

Gene - you have ionization alarms.

Marshall - thanks! 

Kimo - thanks you.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Ok, I didn't realize there were different kinds. However, I did know that like everything else, smoke detectors have a shelf life and need to be retired after 10 years or so.

Posted by Liane Thomas -Top Listing Agent, Bringing you Home! (BROKER Allison James Estates & Homes BRE 01885684) over 6 years ago

Reuben: Not much to add, but a great explanation. Sounds like the dual is the safest way to go.

Posted by Anne M. Costello (Weidel Realtors) over 6 years ago

Liane - you got it.  

Anne - Thanks! 

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Good morning Reuben,

I came over from Kathy's post this morning. In her series she lists posts she learned something valuable from and I missed your post so came over to check it out. She is provide great information and advice about smoke alarms..I now have your post bookmarked.

Posted by Dorie Dillard CRS GRI ABR, Serving Buyers & Sellers in NW Austin Real Estate (Coldwell Banker United Realtors® ~ 512.346.1799) over 6 years ago

Hi Reuben, I'm glad I came over from Kathy's blog. I needed to know this information: that a new smoke alarm is needed every 10 years.

Posted by Sandy Acevedo, RE/MAX Masters, Inland Empire Homes for Sale (951-290-8588) over 6 years ago

Rueben, my husband builds new construction...he is constantly updating and changing alarms....I hate when the batteries are weak and they dont stop making noise.

Posted by Ellen Caruso (Daniel Gale Sotheby's International Realty) over 6 years ago

Smoke Detectors are so important.  We need to be using the most effective devices!

Posted by Fred Griffin, Licensed Florida Real Estate Broker (Fred Griffin Real Estate) over 6 years ago

Rueben, excellent info. like everything else, smoke detectors need to get replacest oo, I have seen too many home with the covers open & the batteries missing.

Posted by Insurance Solutions, Insurance (Insurance Solutions Unlimited, LLC) over 6 years ago

Good info. I had heard about this issue not long ago at an ASHI meeting. 

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) over 6 years ago

Thank you. Thank you. Thank you. I am replacing my over 10 year old smoke alarms this weekend. It sounds like I need the dual mode kind.

Posted by Dana Cottingame (Coldwell Banker Residential Brokerage) over 6 years ago

This is great information, Reuben! I will pay closer attention to it from now on! Thanks for the graphs too--very helpful!

Posted by Peggy Chirico, REALTOR® 860-748-8900, Hartford & Tolland County Real Estate (Prudential CT Realty) over 6 years ago

This is good info. Around here we also need to have CO2 detectors.

Posted by Wayne B. Pruner, Tigard Oregon Homes for Sale, Realtor, GRI (Oregon First) about 6 years ago

Wow, Reuben, a very informative (and possibly life-saving) article.  My wife and I were just talking about the need to upgrade our smoke detectors, and this provides some great insights.  Thanks!

Posted by Matt Robinson, (Professional Investors Guild) over 5 years ago