How do smoke detectors work?


I read this []( but I need help 😛

In: 3

Smoke detectors work by detecting radioactive particles. There’s a little area with a radioactive source, a gap of air, and the detector. As long as the detector receives radioactive particles, the alarm stays silent. Smoke interferes with the particle paths, so the detector doesn’t receive a particle, so it sounds the alarm

There’s a little bit of radioactive metal (usually Americium) in a chamber which releases a little bit of radiation, and a detector which sees this constant little bit of radiation. When smoke fills the room with the detector, some smoke gets into this radioactive chamber and absorbs/deflects the radiation coming off the metal. When the detector starts to “see” less radiation (because it’s being blocked by smoke), it starts the alarm ringing.

To simplify it:

You have a radioactive element (americium) in the detector on one side of a chamber. On the other side of a chamber is a detector. The radioactive source emits particles every so often. If the detector on the other side receives these particles, all good, nothing happens.

If smoke gets into the chamber, it blocks the particles coming out of the americium. So the detector doesn’t detect any particles, and it activates the alarm.

The link is just giving a few details on how the detector actually does that.

There’s two types of smoke detectors, Ionisation and Optical.

Ionisation smoke detectors have a small slightly radioactive substance between two electrodes. The radioactivity crates ions in the air, which can transport a tiny amount of current between the electrodes. If smoke enters the detector, it displaces the air and the ions, and the amount of current drops. A sensor detects that drop in current and triggers the alarm

In optical sensors, there’s a small led or laser diode enclosed in a light tight, but not air tight, compartment. It regularly pulses light towards a photoreceptor, which picks it up. If smoke enters the chamber, it partially blocks and scatters the light and the photocell detects less of it, and again the fire alarm is triggered.

Optical fire alarms are significantly less prone to false alarms, but can trigger slightly later, since they rely on smoke with a lot of soot, and a clean burning flame produces only clear fumes, however, in a real world scenario, any uncontained fire inside a residential home will almost immediately begin burning _something_ that doesn’t burn cleanly, and produce the black smoke necessary to trip the alarm, so the downside is really not that relevant, and the reduced chance of false alarms means you’re less likely to turn of the alarm because it’s annoying you whilst you’re cooking or having a hot shower, an forget to turn it back on again

Here’s a good [Video ]( about smoke detectors