# What exactly sets off a smoke detector? **URL:** \ **Category:** Factual Questions\ **Created:** [November 13, 2001, 6:17am UTC](https://boards.straightdope.com/t/what-exactly-sets-off-a-smoke-detector/93084 "2001-11-13T06:17:58Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![RaCha\_ar](https://avatars.discourse-cdn.com/v4/letter/r/c2a13f/32.png) [@RaCha\_ar](https://boards.straightdope.com/u/RaCha_ar)\ **Post date:** [November 13, 2001, 6:17am UTC](https://boards.straightdope.com/t/what-exactly-sets-off-a-smoke-detector/93084/1 "2001-11-13T06:17:58Z")
I ask this because it is literally impossible to cook in my apartment without the smoke detector going off, unless every window in the place is opened. Today I was doing nothing more exciting than boiling water – I hadn’t even added the pasta to it yet – and the next thing I know, the smoke detectors on _both_ floors of my townhouse are going off. My feelings upon hearing the incessant beep-beeping of these lifesaving devices would be better left to the Pit, but I’d honestly like to know – what the heck has these things on such a hair-trigger? What are smoke detectors detecting, exactly? ---
**Author:** ![GIGObuster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gigobuster/32/421_2.png) [@GIGObuster](https://boards.straightdope.com/u/GIGObuster)\ **Post date:** [November 13, 2001, 7:02am UTC](https://boards.straightdope.com/t/what-exactly-sets-off-a-smoke-detector/93084/2 "2001-11-13T07:02:09Z")
How do they work? > **[How Smoke Detectors Work](https://home.howstuffworks.com/home-improvement/household-safety/smoke.htm)** > > As the saying goes, "Where there's smoke, there's fire." Smoke detectors are amazing: They're pretty inexpensive, but they save thousands of lives each year. Learn all about nuclear and light-sensing smoke detectors. Maybe you should get a different model of smoke detector but the location is the most important factor: [http://www.roswell-online.com/govrment/fire\_dpt/smoke\_de.htm](http://www.roswell-online.com/govrment/fire_dpt/smoke_de.htm) ---
**Author:** ![Hazel](https://avatars.discourse-cdn.com/v4/letter/h/e56c9b/32.png) [@Hazel](https://boards.straightdope.com/u/Hazel)\ **Post date:** [November 13, 2001, 7:16am UTC](https://boards.straightdope.com/t/what-exactly-sets-off-a-smoke-detector/93084/3 "2001-11-13T07:16:07Z")
I have not followed gigobuster’s links, but my guess would be that they detect heat. Just heat. I, too, have had them go off when water was being boiled. But I don’t think the steam is a factor, as they are even more likely to be set of by use of the oven. Turn the oven up above 350 degrees, they go off. The oven door does not have to be opened. Just turn it on, and in about ten or 15 minutes, the detector noise starts. I can’t cook anything at 400 degrees. And the nearest detector isn’t even in the kitchen. ---
**Author:** ![DeadlyAccurate](https://avatars.discourse-cdn.com/v4/letter/d/ac91a4/32.png) [@DeadlyAccurate](https://boards.straightdope.com/u/DeadlyAccurate)\ **Post date:** [November 13, 2001, 2:32pm UTC](https://boards.straightdope.com/t/what-exactly-sets-off-a-smoke-detector/93084/4 "2001-11-13T14:32:59Z")
We had one go off from across a 20’ room by lighting a single incense stick. ---
**Author:** ![VanLandry](https://avatars.discourse-cdn.com/v4/letter/v/eb9ed0/32.png) [@VanLandry](https://boards.straightdope.com/u/VanLandry)\ **Post date:** [November 13, 2001, 2:39pm UTC](https://boards.straightdope.com/t/what-exactly-sets-off-a-smoke-detector/93084/5 "2001-11-13T14:39:21Z")
I have not followed the links either, but I used to work for a manufacturer of smoke and heat detectors, and there is a difference. Smoke detectors work by use of a photo sensor. A small beam of light is projected across a chamber and is ‘detected’ by the sensor. If the beam is broken, the smoke detector will go off. Sometimes dust can get in there this will make a detector go off intermittently for what seems like no reason at all. Heat detectors are exactly that. The internal thermometer reaches a certain temp. and it activates. ---
**Author:** ![SlickUSA](https://avatars.discourse-cdn.com/v4/letter/s/ad7895/32.png) [@SlickUSA](https://boards.straightdope.com/u/SlickUSA)\ **Post date:** [November 13, 2001, 2:41pm UTC](https://boards.straightdope.com/t/what-exactly-sets-off-a-smoke-detector/93084/6 "2001-11-13T14:41:27Z")
they have an element called americurium thatbounces light around inside and when the light is blocked by smoke, it triggers the alarm–i’m perdy sure that’s how they work, or something along those lines. ---
**Author:** ![geepee](https://avatars.discourse-cdn.com/v4/letter/g/ebca7d/32.png) [@geepee](https://boards.straightdope.com/u/geepee)\ **Post date:** [November 13, 2001, 2:58pm UTC](https://boards.straightdope.com/t/what-exactly-sets-off-a-smoke-detector/93084/7 "2001-11-13T14:58:09Z")
They have Americiaum 241 in them well mine does anyway (since its open and batteries torn out since they go off when cooking easily) which reacts to smoke that completes the circuit somehow ---
**Author:** ![Mr.Duality](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mr.duality/32/4098_2.png) [@Mr.Duality](https://boards.straightdope.com/u/Mr.Duality)\ **Post date:** [November 13, 2001, 3:23pm UTC](https://boards.straightdope.com/t/what-exactly-sets-off-a-smoke-detector/93084/8 "2001-11-13T15:23:17Z")
“Today I was doing nothing more exciting than boiling water – I hadn’t even added the pasta to it yet – and the next thing I know, the smoke detectors on both floors of my townhouse are going off.” Could be stuff previously spilled on the burner was ionizing. So, even though you were only boiling water, burned suff was getting into the air and setting off your smoke detector. ---
**Author:** ![RaCha\_ar](https://avatars.discourse-cdn.com/v4/letter/r/c2a13f/32.png) [@RaCha\_ar](https://boards.straightdope.com/u/RaCha_ar)\ **Post date:** [November 13, 2001, 3:29pm UTC](https://boards.straightdope.com/t/what-exactly-sets-off-a-smoke-detector/93084/9 "2001-11-13T15:29:05Z")
> [@](#): > > \*Originally posted by Mr. Duality \* > \*\* > Could be stuff previously spilled on the burner was ionizing. So, even though you were only boiling water, burned suff was getting into the air and setting off your smoke detector. \*\* This has occurred to me. My mother also suggested that the bottoms of my pots and pans might have accumulated detritus that burns when they’re used. Thorough cleaning of both utensils and stove yields the same results. I also have the problem that **Hazel** described of not being able to cook anything above 400 degrees without the blasted things going off. Opening all the windows isn’t a problem if it means avoiding the earsplitting alarms, but since we’re getting into winter I’d like to avoid it whenever possible… Thanks for the links, **GIGObuster.** ::off to read:: ---
**Author:** ![Popup](https://avatars.discourse-cdn.com/v4/letter/p/94ad74/32.png) [@Popup](https://boards.straightdope.com/u/Popup)\ **Post date:** [November 13, 2001, 3:30pm UTC](https://boards.straightdope.com/t/what-exactly-sets-off-a-smoke-detector/93084/10 "2001-11-13T15:30:45Z")
**SlickUSA, VanLandry** and **Hazel**. Please follow **GIGObuster** s link. Most of the smoke detectors work as a small GM-counter, where the ions can get trapped by smoke. I can’t explain it here, but they do not detect heat, nor is there any americurium that bounces light, nor does the smoke break any optical beam (quite the contraty in one less common design). Once again HowStuffWorks have got the Straight Dope. (The only time they have failed me was when they tried to explain GPS, but I’ve already ranted about that elsewhere.) ---
**Author:** ![hibernicus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hibernicus/32/2802_2.png) [@hibernicus](https://boards.straightdope.com/u/hibernicus)\ **Post date:** [November 14, 2001, 11:45am UTC](https://boards.straightdope.com/t/what-exactly-sets-off-a-smoke-detector/93084/11 "2001-11-14T11:45:55Z")
> [@](#): > > \*Originally posted by geepee \* > \*\*They have Americiaum 241 in them well mine does anyway (since its open and batteries torn out since they go off when cooking easily) which reacts to smoke that completes the circuit somehow \*\* The part I have underlined is an example of a widespread problem with alarms in industry. Too frequent, too intrusive or too sensitive an alarm can actually be worse than none at all. **geepee** , I appeal to you to tidy up your posts. I find your posting style quite disconcerting. Feel free to ignore me or write me off as a pedant, but all I’m asking for is proper sentences.