system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 how a smoke detector can detect smoke

If it detected air quality, which is what would make sense to me, how does it specifically know that there is smoke and not something else?
gpt
it depends on the type of smoke detector.  Ionization smoke detector uses a radioactive element and measures the conductivity of the air.  If there are fumes/smoke in the chamber then it's less conductive and puts it in alarm.
photo smoke detectors just use an LED and a light receptor and measure how much light gets reflected off of anything in the air.  They are easy to false alarm with dust or anything fine enough to make its way inside.  I've had spiders set them off before.