Why would a smoke detector go off for no apparent reason?

Battery getting weak, change batteries.

Ghosts playing with matches. Re: ^^^

Humidity, dust, low batteries, dud unit, smoke from cooking, steam from shower/bath or cooking, the list goes on.

Is it also a carbon monoxide detector?

Most carbon monoxide deector have an “alert”.

“GET OUT” is what mine says.

Dust is most likely explanation for a false alarm. Use a can of dust spray to clean all of the detectors in the house.

I vote with @Tropical_Willie. Most battery-drive smoke detectors start chirping as the battery wears down. (Many safety experts recommend changing batteries every time you reset your clock for Daylight Savings Time, so you don’t forget.) Some detectors may send the battery out “in a blaze of glory” (so to speak) as you have described.

Check the detector with the Test button that should be on the face. If the thing doesn’t work at all now, then you know the battery needs to be changed.

Otherwise, take off the face and check for dust, insects, moisture (placement just outside of bathrooms and kitchens are bad because of all the false alarms from steam and “normal” kitchen smoke).

In one house I owned, the placement of the detector outside of the kitchen, and all of the false alarms due to that, caused us to name it the “Supper Detector”.

You let that thing go off for 2 hours? I would have pulled the battery!

I could be caused by a spider, or dust. The idea of the sensor is that if it loses reflectivity, it must be cloudy from smoke. A spider could cause this, if it got in the wrong spot. Dust, or humidity could cause it, and the damn thing going off so long could shake whatever it was lose, but I would be concerned, and replace it immediately.

Maybe your house is on fire, did you check?

I would almost guess that something electrical may have burned out; a DVD player, a lamp, a cell phone charger. I am sure you tried to smell something when you entered the room. There was no trace?

@filmfann The detector that went off is on the ceiling, where I can’t reach it unless I have a ladder. There was no trace of any smoke. This has happened once before.

@ninjacolin No fire.

are you sure? generally fire alarms go off when there’s a fire.
maybe double check. it’s not something you wanna be wrong about.

@ninjacolin As a property owner and manager, I can tell you from my experience smoke detectors are:

1. Not fire alarms
2. Are prone to go off for a variety of reasons (many of them listed above)