Last updated on November 16th, 2018
Smoke detectors expire. Over time they lose sensitivity. The last thing you want is a weak smoke detector in your room while sleeping soundly at night.
Here’s what you need to know…
The smoke detector ‘works’ largely unnoticed while on the ceiling or walls while it constantly and continuously measures the air around it – just waiting to alarm.
It works hours, days, weeks, months, years – never ending.
At least until one of two things happen…
1. The batteries run dead.
2. It’s shelf life expires.
Note: A good habit to get into for replacing smoke detector batteries is during every New Year. January 1 seems like as good a day as any…
But did you know that smoke detectors lose their effectiveness over time?
The U.S. Fire Administration says most smoke detectors installed today have a life span of about 8-10 years. After this time, the entire unit should be replaced.
It is a good idea to write the date of purchase with a marker on the inside of your smoke detector’s (battery compartment) so you will know when to replace it. Some of the newer detectors already have the purchase date written inside.
UPDATE 1
Someone asked why there’s a 10 year shelf life when the shelf life of an ionization smoke detector’s “Americium 241” has a half life of over 400 years. Good question.
I suspect that the NFPA recommendation may have to do with electronic components aging and/or the reliability thereof. Electrolytic capacitors ‘dry out’ for example. Also, a dual sensor smoke alarm additionally includes a photoelectric sensor which may be affected over time.
UPDATE 2
“It is the sensors that fail after a given amount of time, not so much the electronic circuitry or the radioactive ionization source. The sensor modules rely on an electro-chemical reaction to smoke/CO, they get saturated over time depending on exposure and also just plain start breaking down.”
About Smoke Detectors (Important!)
There are many different brands of smoke alarms available on the market but they fall under two basic types: ionization and photoelectric.
Ionization alarms sound more quickly when a flaming, fast moving fire occurs.
Photoelectric alarms are quicker at sensing smoldering, smoky fires.
Dual Sensor alarms combine ionization and photoelectric into one unit.
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, you might consider installation of both ionization and photoelectric or dual sensor smoke alarms.
The Best Dual Sensor Smoke Alarm:
The following smoke alarms are what I have installed in my own home. I have several of the AC (hardwired) units and I’ve also added a few battery powered smoke alarms in other locations.
AC Powered (hardwired) with battery backup
More: Dual Sensor Smoke and Fire Alarm, and Why They Are The Best
Fire Escape Plans
You should have escape plans and make sure everyone in the household knows them.
Fire Extinguishers
Have several fire extinguishers!
Consider one in the bedroom and one near the kitchen (at least!).
You should also install a Carbon Monoxide Detector!
Carbon monoxide is winter’s silent killer.
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I am in a state that still, who knows why, changes time each year.
I change all batteries in clocks, safe, smoke alarms, etc. the fall at time change.
I also test my smoke alarms, by using smoke, twice a year and replace as needed.
I just replaced my alarms. Two photoelectric for smoke, one CO2. The old alarms seemed to be fine but were about seven years old. Put the replacements as high as I could. Both smoke and CO2 rise.
I knew, and know, that there are two styles of smoke alarms. Both have pros and cons. Kinda wondering why anybody would want an expensive alarm that does both.
“Kinda wondering why anybody would want an expensive alarm that does both.”
Relying solely upon photoelectric (which is very good at detecting smoke) will leave some vulnerability to a hot fire (which inherently produces less smoke than a smoldering fire). This is where ionization detectors excel (detecting hot fires). Additionally, hot fires tend to move much faster leaving less time to escape.
To have the best of both worlds, you could literally mount two separate smoke alarms — one of each type (ionization and photoelectric) or you could mount one which has both sensors built in (dual sensor). The price relationship generally seems to be similar (two individual smoke detectors versus one with a dual sensor).
In addition to the two types of smoke detectors, a carbon monoxide detector is an advisable third detector.
Ken,
this talk about various types of detectors…
am wondering if folks understand that Carbon monoxide (CO) is big concern and the detectors should be placed low to floor, as this falls (that is what the fire department says), right?
The ‘specific gravity’ of carbon monoxide is nearly identical to air, 0.9657. I’ve read that it doesn’t matter terribly if on the floor, wall or ceiling — but follow manufacturer instructions.
However, this is what I do — I definitely keep one in the bedroom (I want to be awakened!). If more than one, then spread them around in other rooms. Since carbon monoxide is ever so slightly ‘lighter’ than air, it will (ever so slightly) tend to rise – especially with any heat drafts.
Some CO detectors are built into smoke detectors (all-in-one), so those type of units should be mounted on the ceiling as per instructions – the same as a conventional smoke detector.
Any other opinions out there?
Because the photo type won’t respond to the heavier black smoke caused by petrol-based materials commonly used in today’s furniture and construction, they often don’t pick up a serious fire in time to allow escape, the ionization is a better choice. The dual is better still. Sadly, the only ones required by some codes are the photo responders. Scary.
Smoky, you’ve got that somewhat backwards. Photoelectric devices are much better at detecting the large dark particles produced by a smoky fire. Ionization-type detectors work best with fires which produce small highly ionized particles – ie hot and bright later-stage fires.
The typical scenario where an alarm saves lives is the night-time smoldering fire. Photoelectric detectors do a much better job of detecting this sort of fire than ionization detectors.
Each type detects a certain type of fire better. Ionozation detectors work better for quick moving/burning fires. Photoelectric, work better for smoldering/smoky fires. Rather than “guess” or try to rationalize what type of fire you might have in YOUR home, where YOUR family lives, you would be better protected having detectors that do both! THAT’S why! Also CO2 is carbon dioxide. I think you mean CO, and it doesn’t rise like smoke. Just put them in each level/floor/part of your house that you can live in, especially in or near the bedrooms, and you will be covered.
My smoke detector is permanently wired in. I am not sure if there is a battery back up. It has been there for at least the 5 years I have owned the house. Does that need to be replaced? I live in a very small town and the nearest electrician is over 40 miles away.
PS. I also have a CO detector. I change the batteries in that.
The U.S. Fire Administration recommends replacing them in 8-10 years. To answer your question, maybe you could find out the history of your home prior to you having purchased it – which may provide a clue as to their age.
Look for a date on the detector. Most brands and fire agencies recommend replacing them after 7-10 years! Look for a battery too(some have batt. back up) and they seem to get forgotten about in these units.
Some of the hard wired will “unplug”. If someone that you trust knows how to do this, then takes them to the store, they usually can just get the right newer ones, and replace them. When in doubt, get an electrician that works on fire alarms!
Good luck, and be safe!
Daisy ,yes, it will need replacing. can’t recall how long they last, but it should have an expiry date on it. to see if it has battery backup, take it down, and actually look in the battery compartment. ours had the compartment but no battery.
these hard wired in detectors actually plug in. so get a ladder and get up there, you should be able to see the plug. if not, call the company and as them/look on the net.
first time we had ours replaced, we understood that hard wired in, meant that. we called an electrician. of course he did not tell us different, and likely laughed at us.
however, it is a simple plug. unplug, take it to the hardware store. ask them which model /same model to replace.
No it is not. the part that needs to be replaced is removed. the plug attachment stays the same.
I just replaced a couple of the hard wired ones which were…due. The Kidde’s I used (from a big box hardware store) had a couple options for the plug attachment, so no problem with failure to fit……
Ohhh… forgot to add. I also installed standard battery ones nearby (in addition to the hard wired ones) because two is one, right?
I replaced 2 detectors in January.Brand new ones.And thank God I did! Last Thursday,in the middle of the night,my pellet stove malfunctioned causing a fire.Fortunately,the dectors worked like a charm,and I was able to control the fire.Could have been totally different had I not replaced my old ones!
We have ours hard wired into the house which also has a battery as a back-up. The good thing about the hard wired units is that if one goes off, they all go off. So the kids are downstairs sleeping and if the woodstove should malfunction and start a fire, they will know because their smoke detectors will go off as well as all the others. Even if the power goes out they will still work that way as the batteries will take over and set off the other detectors if needed.
Peanut_gallery, the hard wired ones are ok, but we have some regular ones too (ok call us obsessive)…Somehow, have always worried about the wired ones failing.
another thing, the hard wired ones have a definite expiry date.
also,
have you ever actually looked inside yours to see if there was a battery in them? good idea to do so.
our hard wired ones failed, many years before the expiry date. (they are brand name ones). hubby took them down, and looked to see if the battery needed replacing. there was no battery. there was an empty spot, with cover, but no battery connections. phoned the company, and they said, yes this model is made like that.
Yes these are newer ones and the battery cover is on the front, so you don’t have to remove the smoke detector in order to change the battery. We actually had a major power surge last summer where it blew out the electrical panel as well as our furnace. When that happened, we lost power to the house and the plastic housing on the furnace motor started smoking. The smoke detectors worked as designed. They have come a long way.
Sadly I don’t need to “test” my smoke alarms, I seem to set them off inadvertently quite often cooking! I have never caught anything on fire, but I guess the occasional light smoke is enough to set them off. At least I know they work!
A running joke at our house. The alarm goes off and dinner is nearly ready! Usually I just holler, “Susie Cooks.” Then I get the look. Oh well, she keeps cooking and I keep eating. Works out well, except when dish duty comes around.
My husband just keeps delaying the installation of new batteries; despite the fact that I buy them, leave them out, and remind him.
He seems to prefer getting awakened in the middle of the night to respond to the incessant chirping. Several months ago we experienced this, except the smoke alarms were not chirping, but blaring. There was no sign of smoke or fire. We spent the night replacing batteries and hitting the re-set button, rotating between the 8 smoke detectors throughout the house! I even sat up with a long pole to re-set the one in our room that just wouldn’t stop!!!
The next day, although sleep-deprived, my brain suggested that maybe it was time to replace all the smoke alarms. They are original to the house. We’ve lived here almost 10 years and it was 3 years old when we bought it. Went to Home Depot and found 2 packs of 4 smoke alarms each. Spent the evening installing and haven’t been chirped at since.
Great thread here. I’m a Firefighter and owner of a smoke detector installation company. Most of the major points have been addressed. In case no one read the owner’s manual of the new detectors, most major brands (Kidde, BRK, First Alert, Fire X, etc) have a hush feature so when you do burn dinner, you can just push the button on the cover and silence the alarm for 10 minutes. Hopefully that is enough time to clear the air or else you need give up on cooking all together. Also, I don’t know why they still make wired detectors WITHOUT battery back-ups but don’t ever ever ever buys those. It’s usually about $1 more to buy the same detector but WITH a battery back-up. Totally worth it.
Jon, so right about not buying without battery backup…That is what happened to us. Detector started beeping, for no reason, (even though it had yrs left to expire)..when hubby took it apart, thinking to put a new battery in, NO Battery, or battery connections. from the outside, though, you could not tell there was no battery, as it HAD a battery compartment.
hubby emailed the company and they never did respond.
(all we now have have the battery backup.
I thought my dual smoke detectors worked fine because every time i made toast they would go off! Everyone joked it was an automatic dinner bell! But then my dishwasher caught fire. There was smoke hanging 3 ft. off the ceiling and flames shooting out from under the cabinet! CRICKETS! Not a sound out of any of them!(but they went off again the next day when i was broiling) Batteries – good. Test button – works! The smoke detector was 7 yr. old. We immediately replaced all of them, hoping that solves the problem. (Fingers crossed and not having much faith). PLEASE REPLACE OLD DETECTORS! You can’t trust them.
What is the effect of smoke test spray if we use it after two months on smoke detector for its pm…
Is a detector’s shelf life different from its service life? That is, is a unit’s life determined by date of manufacture or by the date it was actually put into service? If a unit sits on a shelf for five years, then is actually put into use, is it considered good for another five years, or for ten years of actual service?
I would also like to know if a new smoke detector (still in the package) that I bought quite a few years ago, is still good to start using. It has been in storage in my cool basement, and I just forgot it was there. The plastic clamshell packaging was always sealed, but the batteries (in a separate part of the package) had white powdery stuff on the top and obviously eroded themselves or whatever, and I threw them out. There is a sticker on the bottom of the detector that reads: “2002 Dec 23” which I am guessing is a production date. The recommendation I am hearing on this website says to replace after 10 years. Is that from the day I start using it, or from the day of the product label (production date:). I dont understand what would “wear out” when it hasnt been used..
Your 2002 detector is no longer reliable. It is now 13 years old. I would not trust your life on an expired smoke detector…
It is the ‘detector’ itself which has a shelf life – not the electronics…
They expire because most detectors rely on a very small radioactive material (Don’t worry its safe as long as you don’t take it apart and play with the components) americium-241, to detect those minuscule amounts undetectable to us humans. The radiation is decaying constantly until it becomes useless in the detector. That is when it needs replaced. If you smoke foods, tobacco, or even paint near your detector you decrease the ability of the detector to work. If you do these things, replace your detectors sooner than 10 years.
the half life of Americium is 432.2 years. I think I’m good.
Our house is 11 years old. We have wired in smoke detectors with battery backups. We now have two of those detectors that chirp like the battery is low but when we put new batteries in, it doesn’t stop the chirping. Do the dectectors need replacing?
@Nita22, If you home is 11 years old, it is certainly recommended that you replace your smoke detectors.
I can appreciate why ionization smoke detectors expire due to the 1/2 life of the radioactive material used, but why would photoelectric detectors expire? Likewise CO detectors?
Where would the date be on my detector? It is wired in and does have a battery. It has chirped all night in spite of my changing the battery. Thanks.
Re: Smoke Detectors with ‘plugs’…
They will NOT set off other detectors unless they are ‘networked’ together. That is to say that there has to be a wired connection between each detector, usually 14/3 ROMEX, inside the ceilings and walls.
Take a look at your plug – you should see three wires going into it. In ROMEX, the Black (hot) wire and the White (neutral) wire supplies the 120 volts AC to power them, while the red wire is what ties them all together. The green (or bare copper) wire is the ground, but is seldom used in detector wiring circuits.
The detector wiring that goes to the plug itself will not necessarily have the same colors, so double-check your installation instructions to get unit specifics.
And yes, definitely spend the money and get the ionization/photoelectric dual-detection ones with battery backup. There’s no guarantee that your fire isn’t going to affect your detector wiring, especially if you experience an attic fire. What’s a few extra bucks compared to a life?
It’s better to be safe (and alive) than sorry!
My smoke alarms are 20+ years old, I regularly test them using actual smoke, 1 match lit and then blown out in the room they are in is enough to set them off.
The shelf life of an ionization smoke detector is clearly not related to isotope decay. Americium 241 has a half life of over 400 years! So why then? Possibly dirt accumulation fouling the sensing area? A bit of a stretch. Most likely an industry standard to ensure repeat sales.
I suspect that it has more to do with electronic components aging and/or the reliability thereof. Electrolytic capacitors ‘dry out’ for example.
Additionally, there may or may not be push from the NFPA to upgrade to the latest (presumably better) technology after 10 years. Just speculation.
Ken,
It is the sensors that fail after a given amount of time, not so much the electronic circuitry or the radioactive ionization source. The sensor modules rely on an electro-chemical reaction to smoke/CO, they get saturated over time depending on exposure and also just plain start breaking down. Had a boss who used to demonstrate a underground CO monitoring meter by blowing cigarette smoke into it, finally over-loaded the sensor after about a year of doing that weekly and had to replace the whole sensor module. We replaced our house smoke/CO detectors after 7 years when they started going off errantly.
Minerjim, Thanks for insight into the question as to “why”. I’ve updated the article to include your explanation.
Ken,
Yeah, I had to say something instead of just letting everyone keep guessing as to why they go bad. Main thing is there is a good reason they do go bad, and to be ready to replace them. Sorry for being the ‘Anal Engineer’, I have just lost too many friends to CO it depresses me.
The fire code for my city in Ca. is a smoke detector in each bedroom, one in the hallway leading to the bedrooms, and a co2 detector in the hallway.
If you pull a building permit for anything, the city wants to come in the house and check for the smoke detectors location. Overkill???? No, as a retired FF/Paramedic the FD is trying to be pro active. Years ago we installed smoke detectors in dwellings for people that could not afford them.
Keep Safe.
Kevin McDowell;
That’s actually now in the National Fire Codes or NFPA Codes, that’s ALL new construction has to meet, In addition all new Business License Applications require a Fire Inspection of the Building before they will issue a Licenses.
Good, Bad or Indifferent, probably not a bad idea.
NRP, Kevin McDowell,
Actually having CO detectors in residences that have fuel burning appliances has been part of the IRC (international Residence Code) since 2009. This building code is used extensively across the US. The newer code calls out where in the residence, usually in or outside of sleeping rooms. Garages are now required to have smoke/co detectors in them . Also must upgrade to have them for remodels. It is one thing I can think of that the Gov’t has done that actually has some smarts behind it.
‘Smart’ article, thanks.
Time to replace the 8 detectors in my humble 1800 SqFt home. Even have 2, yes two, in the Craw Space under the house.
Mine are 10 years old, guess I should have read this back in 2014???
Yes I’m paranoid about fires, When is the last time y-all had your Fire Extinguishers Checked/Tested?
As Ken recommended, have a couple of Extinguishers in the home, and KNOW how to use them…..
Good subject for me. We are camping in our RV and the smoke detector went off the other night for no apparent reason. I pulled it down and removed the battery and it was still alarming. Then I noticed that the propane / CO monitor
was the one that was alarming. Not the first time that it has done that and the dealership couldn’t find a problem with it. I would not get it to shut off and the propane tanks were turned off. Apparently it is hard wired into the trailer. I pulled every fuse and through every circuit breaker in the box and it still kept alarming. I had to cut one of the wires to get it to shut up. That was tree days ago and we are still alive so I guess there was nothing wrong with they systems in the trailer.
The smoke alarm has been problematic since we purchased the RV about 2 years ago. Turn on the heater and it goes off, make toast and it goes off. Very annoying. Anyway i was frying potatoes the other day and my wife comment on how smoky it was. No alarm going off. Makes me wonder how old the alarm was when it was installed. Time for a new one. Thanks for the reminder.
I replace the smoke detectors every 3-years. They cost $5.00 and are easy to swap out.
Smoke detectors are not expensive.
Having a couple spares should not be a burden, along with batteries.
Hard wired detectors are not wise , IMO.
The article title is misleading, the author used the terms Smoke Detector and Smoke Alarms interchangeably, they aren’t.
Smoke Detectors are connected to an Alarm Control Panel, installed by an alarm company, inside your residence or in a multi-family dwelling with a large commercial Fire Alarm Control Panel, if this is the case the 10 year replacement rule does not apply, unless the manufacturer says otherwise. Don’t touch, call the building owner.
The rest of us have 120vac interconnected “Smoke Alarms”, that must to be replaced every 10 years. The Ionization detectors are so last century and they are radioactive hazardous waste, think about it.
The Photoelectric style are very very good at false alarm discrimination and are usually combined with a CO detector and a lifetime 10year battery with options for a verbal alarm, emergency lights, wireless mesh networking, home automation integration features, and mobile app notification…
Senior Fire Alarm Tech;
Please correct me if I’m incorrect,
Does the little white thingy up there not “detect” smoke? and does it not give an alarm when it “detects” smoke or other such “stuff” in the air? Hence the ‘common’ name of “Smoke Detector” or “Smoke Alarm”? Remembering if it’s a Tomato or a Tamato, so long as ya HAVE a “Smoke Thingy” in the home.
I will agree 1000%, replace the “little White Thingy” if over 10 years, and take it to a radiation hazardous waste disposal site.
Thanks for clarifying the semantics. It’s funny because for this article I purposely chose the phrase “smoke detector” (whereas other related articles I’ve used “smoke alarm”).
The reason I did that in this case was because the common “Joe” (sorry Joe) out there use both phrases interchangeably. So I decided to mix it up a little.
Given your expertise, I’m curious why the commercial smoke detector as you describe (just a detector – not an alarm) which interfaces with a master fire panel – does not fall under a 10 year shelf life. Different materials used?
By the way, I adjusted the post title to read, “Caution: Smoke Detector Alarms Have A Shelf Life” 😉