7mo ago

what invisible thing could set off my smoke detector?

(I have carbon monoxide detectors that are not going off)

I have smoke detectors that are incorporated into my home alarm system. The other day, the one by my front door went off for no apparent reason, twice, and when I changed the batteries, it started alarming again immediately.

there was absolutely no reason for it, there were no open windows or doors nearby, it just went off. so, my alarm company replaced it. installed the new smoke detector yesterday and... it just went off again. completely different smoke detector.

there's absolutely nothing in my house that could produce carbon monoxide, but I have separate CO detectors anyway that aren't going off. there's no smell, there's nothing visible, and these are those ~~electro optical~~ photoelectric style ones.

83 comments

I found it amusing that these posts were adjacent.

Call the fire department, they have detectors that they can use to look for gas leaks and other things that can set off a detector.
You can also call your gas provider. One of those two should be able to track it down, it could be a lot of things, but two different smoke detectors going off in the same location is a huge red flag.
Best case, you have something kicking up fine dust, worst case, you have a smouldering electric fire in your wall somewhere.
Don't panic, but also do not ignore this.
- The weird thing is, it alarmed three times in its current position, but when I changed the battery, it started alarming in my hands in a completely different room, which I already had two other smoke detectors in it that weren't going off.
  and there's no gas. I live outside Miami
  
  This makes it sound like it's probably just a defective detector. Swap it with one that hasn't been going off and see if that one starts going off too. If it doesn't then odds are something just failed in it.
  You could also just try blowing some air through it to blow out any dust. But it shouldn't be that dusty after only a year so I'm still leaning towards defective.
  
  ~~Sounds like a bad unit, try replacing it. The fact it’s going off elsewhere and no other detectors go off says it’s the unit.~~
  I missed that you changed units, check your wires.
  If the new unit starts going off, you may have a switched wire between your signal (red) and your hot (black) that fried the unit.

~~Look for an expiration date. Radionucleotide style detectors end up failing with false positives when they reach end of life. You might need to have all the old ones replaced.~~
- I used the wrong word, but this is a photoelectric detector. The manufacturer date is less than one year ago
  
  Sorry, I must have skimmed too quickly and missed that.

I don't think this is what you're experiencing, but I had an alarm go off randomly for one beep once. Went and looked at it, and a few seconds later a spider crawled out and away from it.
If it's photoelectric, anything that could scatter light could cause it to go off. Is your house dusty?
- not particularly, and this one is the closest to my air filter. they're replacing it one more time, and I'm going to put a security camera on it this time lol
  
  If you're going to the expense of putting a camera on it, why not take it a little further and slap together an arduino-based sensor suite with some logging? See if you can find any correlations in temp/humidity/gas conc that might help with diagnosis.

Mine went off in high humidity when I showered and forgot to turn on the fan
- I thought of this one too. "Photoelectric" smoke detectors are a thing, and it's good to know if that's the kind you have.
- thing is, it's the smoke detector farthest from my shower, and only the third time it went off was anywhere near a time that I had showered.

I’d call the fire department to ask them to come out and make sure that there’s not anything slow burning that’s hidden in the walls. Be sure to mention two separate smoke detectors have been going off. Even if that’s not what it is they’ll be fine with coming out to check.
- Anecdotally, when I was a kid, we had an electrical issue wherein a short or something was causing wires to slowly melt through their jacket, inside the wall. It was triggering smoke detectors, but we couldn't see or smell anything. Fire department came out and found it, but if we'd ignored it, it almost definitely would have been a huge house fire eventually. Definitely second this advice. It doesn't cost anything to have them come look.
  
  In my first apartment, I had a smoke detector that was mains powered. The wire metals weren't compatible and eventually the wirenuts burned and cut off power to half the room. The smoke detector's wires were all burnt up. It never alarmed unfortunately so I only learned about it when half the room just went dark. That could absolutely have turned into an electrical fire.
  Definitely worth getting it checked.

High humidity can cause them to go off as well. Used to use a cool air humidifier in our kids' room at night and had to stop because it would eventually set the alarm off.

I've had a photoelectric alarm set off by steam from a dryer in the next room, through a closed door.
- That's why I don't understand why a ton of hotels have no bathroom vent fan, and photoelectric detectors within feet of the bathroom door.

I need to replace a set of expired smoke detector at my elderly parents' house. They're too old to have alarms going off in the middle of the night just because the wind blows.
Yet, Amazon only seem to sell ones with photo-electric sensors, and many reviews complain about over-sensitivity with dust, and under-sensitivity when the room is clearly full of smoke.
Additionally, the ones with sealed 10 year batteries - many reviews report a battery life of 2 years or so in practice, with increased false positives as battery life runs down. So now, they have to replace whole units rather than just batteries.
What happened to good old ionizing smoke detectors with 9v batteries that needed replacing every 2 years or so?!
- Have you tried driving to the store?
- so the other brand I have in my house, I've been very happy with. First Alert combination smoke and carbon monoxide. The only improvement they've made is that it runs on AA instead of 9V (I'm pretty sure my smoke detectors were the only reason I was keeping 9 volt around the house anymore), and you can slide the battery tray out without removing the detector so you can disable the alarm and replace the batteries without even having to take it down
- Spend a bit more on UL approved brands, those tend to be more resilient to dust.
  Photoelectric type is better for home use as your typical fires are smouldering, which photoelectrics are better at catching.
  Here's a deep dive if you're interested https://youtu.be/DuAeaIcAXtg

Spiderwebs or insects can mess with the sensors, likewise with dust. Try spraying some canned air inside. Or if it's a few years old, you may want to replace it.
- Firefighter here. Brush and gently vacuum your smoke detector. Insects are attracted to the LED and can set off the alarm. They may be very small. Dust can also set it off.
- now there's an idea. I live in south Florida and my house was built in the 1950s. I wonder if some spider has decided that the inside of this detector is a good place to hide. blowing it out isn't going to help though, because I replaced the entire detector and if there's a spider going in there, they just went back into the new one immediately. I'm going to have to set up a security camera on this thing
  
  I used to live in Miami and I had a detector do that. Maybe it's pollen? There's a shit ton of weird-ass pollen in Miami.
- The instructions for my smoke detector recommend spraying the openings with compressed air regularly.

A ghost 👻
- I wish he'd come over and tickle my balls instead of tickling my smoke detector
- Had to scroll way too long to find the right answer.

Dust maybe? Dust can have the same particles as smoke.
- I second the dust. Dust can collect on the sensor and trigger the alarm. You can try vacuuming or using a compressed air cleaner, or just replace.
  
  this is a brand new smoke detector. it's all up in the original post

I've set one off while dying my hair.

I think you said elsewhere that they are new and that they are photoelectric rather than the radioactive ones.
I'm purely taking a shot in the dark but I'm wondering if you should try sealing up the hole(s) in the wall that you made to run electric and to mount the detector
My thinking is that dust might be getting caught up in a tiny draft through that hole and it's so close to the source that it sets it off. Cause like, if wind hits the side of the house, there can be some positive pressure in the crawlspace which often also means inside the walls.
I guess maybe somehow there could be some stream or condensation as well. If it's right by the front door and the humidity is high, maybe the hot air from outside meets the AC air and causes a tiny amount of condensation. Or if you live in hellscape temperatures, maybe there could be some vapor generated because of the hot air.

Are they Kidde? I've had 3 photoelectric Kiddes that started failing and going off randomly. I've been slowly replacing all of mine.
The builder installed them. Occasionally walking through our neighbourhood we hear other people's going off too.

I have set off smoke detectors with a power washer and with saw dust

update - so I've got two more diagnostic steps. I have another detector of the exact same brand in another room, I'm going to switch them and see what happens. if the detector from my kitchen starts going off by the front door, then I'm going to try another brand that I have elsewhere in the house and move forward from there.
- It could also be an issue with the wiring if they are interconnected
  
  they're connected to the base station wirelessly is all

Does anyone in your house vape?
- Vapes don’t trigger traditional alarms
  
  They will trigger a laser alarm though. Depends what type of fire alarm you have. I have a laser alarm in my house and if I open the bathroom door too quick after a shower the steam can even trigger it.
  
  They also don’t produce invisible results
  
  My partner’s vape triggers ours https://www.kidde.com/home-safety/en/us/products/fire-safety/combination-smoke-co-alarms/KN-COSM-IBA/

Might be worth buying an infrared thermometer to see if there is wiring overheating in your walls. I'm not an electrician but i wonder if it's something then can happen sporadically such as if there is something drawing a lot of power that turns on/off. There are inexpensive ones out there and they can be handy to have around.
- I'ma show this to my wife the next time the smoke thing beeps as an excuse to get a fancy new thermometer.

Since it went off in your hands, have you tried googling the make and model to see if there are any similar complaints or even recalls for them?
- they're replacing it one more time

Does it get hot by your front door or in direct sunlight? We have a few in my house that go off if our kitchen gets too hot. We had to move them down the hall slightly and they stopped. A really old one we have upstairs, hardwired into the house electric (built in 86) trips if too much steam builds up in the bathroom and let's loose into the hall.
- it doesn't, my house is outside Miami so it's well designed to prevent direct sunlight from any of the windows.

They are probably both about the same age and need replacing. Smoke and carbon monoxide detectors have a finite lifespan, no matter how often you change the batteries. Fortunately they're not all that expensive, just get new ones. I had the same problem in my apartment last year, and the carbon monoxide detector was over 10 years old. So they just replaced it, problem solved.
- so, my alarm company replaced it. installed the new smoke detector yesterday and… it just went off again.
  Nice theory but it's disproven by OP's initial text
  
  I think he's trying to say that maybe they sent me a new detector that was just as old as the old one, but they didn't
- I've had the first detector for like 5 years and the second had a manufacture date from about a year ago

Some newer (in the last 10 years) smoke detectors use an infrared sensor to detect fire as well as smoke, and it may be going haywire off a reflection of the sun, or intense heating of a spot within its detection area.
If you can, borrow a FLIR or infrared camera and check the area when the detector goes off.
If you post your model of smoke detector, it would be easier to tell if it has this feature.

I had trouble with them going off in humidity, they were past their expiry date so replacing them fixed the issue.

omg 😭😭😭 The new detector went on off in the living room where the old one did. switched it to the kitchen, put the kitchen detector in the living room, and the new one went off in the kitchen. wtffff
- Sorry, trying to follow here. Three locations: front door, kitchen and living room. 4 detectors: original front door, new front door, kitchen and living room?
  Original front door went off in situ and in the living room while holding it?
  New front door went off at front door. Swapped NFD with living room - NFD went off in living room.
  Moved NFD to kitchen and it went off in there too?
  Where are the K and LV detectors now? Have any of those gone off anywhere in the house? Are THEY functional? (Sorry if you already said, I’m trying to piece the bits together and mighta missed that)
  
  three detectors. front and living room are the same place. but I'm getting one more replacement to check

Are they networked? Mine are somehow connected and the one that beeps doesn't always seem to be the one that detected the issue.
- they are networked, wirelessly, but one won't set another off. they will set the base station off, as if my burglar alarm has been tripped. also, my system will tell me exactly which smoke detector went off

Did you open one up yet? That might give you a clue 🤔
E.g. I don't know exactly how wide the gaps are, but here it looks like small insects could get in. Maybe you have another problem than smoke 🫣
- a spider could absolutely crawl through the grading over the detector portion. these are under warranty from my security company, so I've held off on disassembling one but I will eventually

Are your smoke detectors linked to each other? Could be faulty wiring in the circuit, or a completely different smoke detector failing and sending out an alarm that triggers the others. The latter happened in my home when I was growing up: the living room smoke detector kept going off a few seconds before the rest of them would chime in, but it turned out it was the one in the nearest hallway that was failing and sending out bad signals. The living room detector was just the next in the circuit.

What country? AFAIK in the US you can't make the batteries replaceable. If they are wirelessly linked they can have auxiliary batteries for that, but (I believe) that's different than the main battery...
EDIT: I seem to be thinking of California, maybe not all of US.
- It's the same here in New Jersey, or at least the city I'm in. Recently a fire inspector came by the condo building I was living in & failed ~ 60% of the units because they still had the old style replaceable battery smoke detectors. Apparently going forward we are/were supposed to be using sealed battery smoke detectors & replace them entirely every ~10 years when they stop working.
  EDIT: Not sure if that's OP's problem unless their alarm company is so cheap that they keep giving OP really old detectors to replace with.

Have you ruled out other types of fumes? Eg fresh paint, perfume, scented oil diffusers etc.
- yeah I'm autistic so i can smell that shit a mile away

Depends on what kind of detector it is but alot of them use small amounts of radiation and a detector that triggers when the number of particles detected drops below some level.
How smoke detectors work
That being the case any particulate large enough to interrupt the particles could cause it to go off.
For example high humidity misty water from a shower wafting over a detector placed over the bathroom door, etc.

Try replacing the batteries. That's often the reason for this type of thing.
- as stated, as soon as I replaced the battery it started alarming immediately so I replaced the entire detector and it's still doing it
- AFAIK in the USA you can't have the main batteries be replaceable (I think an aux battery for wireless functions is allowed...).
  EDIT: I seem to be thinking of California, maybe not all of US.

83 comments