all 7 comments

[–]Icy-James [score hidden]  (6 children)

I’m assuming it just tests if there’s enough juice in the battery to make the beeper ring. As far as I’m aware, most smoke detectors use a tiny radioactive source that emits alpha particles (which can be absorbed by a few metres of air or a thick sheet of paper) and a detector to detect those alpha particles. When smoke gets in the gap, it blocks the alpha particles from reaching the detector and that’s what sets off the alarm. That’s why I don’t think the the test button tests whether the sensor works or not - only the battery, but I could be wrong. I guess if you want to test the sensor then get a candle underneath

[–]Gnomio1 [score hidden]  (1 child)

Broadly correct but it’s slightly simpler than that.

They don’t actually detect the alpha particles (from the 241Am source). The alpha particles ionise the air in a gap between two plates, a very small voltage thus exists between the two. As you said, smoke stops the alpha particles, so the voltage changes, the alarm goes off.


[–]Icy-James [score hidden]  (0 children)

Ahhh I see, very cool! thank you so much!

[–]ItsLikeRay-ee-ain [score hidden]  (3 children)

Do not put a candle underneath a smoke detector. Large fires have started that way when they set the smoke detector on fire.

[–]Icy-James [score hidden]  (2 children)

Im hoping they would have enough sense to not literally put the flame so close as to burn the smoke detector lmao

[–]we_need2talk [score hidden]  (1 child)

Also, if you want to test it, you would blow the candle out first and then let the smoke waft up.

[–]Icy-James [score hidden]  (0 children)

I was hoping that was implied too but maybe not lmao sorry