How Smoke Detectors Work

Published by
May 26

Bill takes apart a smoke detector and shows how it uses a radioactive source to generate a tiny current which is disrupted when smoke flows through the sensor. He describes how a special transistor called a MOSFET can be used to detect the tiny current changes.
Video Rating: 4 / 5

First Alert Photoelectric 10 Year Battery Smoke Alarm,SA700LUK

  • Product code : PIKFT7001
  • Brand : First Alert
  • Manufacturer part number : SA700LUK
  • Barcode : 5022391064152
  • PLEASE SEE PRODUCT DESCRIPTION BELOW FOR MORE INFORMATION
10 year long life sealed in lithium batteryPhotoelectric "Optical" technology reduces nuisance alarms caused by cooking smoke and steamTest button for weekly alarm testingHush button silences nuisance alarmsLoud 85dB alarmLow battery warningWall fixings included10 year guaranteeCertified to BS EN 14604: 2005.

List Price: £14.99 Price: £12.99

Post to Twitter Tweet This Post

Related posts:

  1. First Alert Photoelectric 10 Year Battery Smoke Alarm,SA700LUK
  2. Choosing And Installing The Right Smoke Detectors
  3. Why Hardwired Smoke Detectors Are The Very Best
  4. Smoke Detectors – It’s Really Vital to Conduct Monthly Tests
  5. Where Do You Install Smoke Detectors?
Filed under: Smoke Detectors, , , , , , ,

21 Responses

  1. thomasthuyaaung Says:

    I really love your videos

    Posted on April 8th, 2011 at 7:20 am

  2. crasherball Says:

    I literally understood nothing in this video lol

    Posted on April 8th, 2011 at 7:34 am

  3. TheJonititan Says:

    Optical detectors are also quite interesting.

    Posted on April 8th, 2011 at 8:12 am

  4. TheJohn8765 Says:

    Damn, I was asked this exact question a week ago. I was struggling to explain the specifics. If only I’d consulted Youtube.

    Nice vid.

    Posted on April 8th, 2011 at 8:57 am

  5. timerider4 Says:

    Using a small amount of radioactive material to build a detector that senses smoke? That seems overly complex, and it wouldn’t seem like it would work reliably.

    Posted on April 8th, 2011 at 9:17 am

  6. Rehabilitator Says:

    I’ll be honest, I pronounced it a-me-ri-ki-um.

    Posted on April 8th, 2011 at 9:43 am

  7. junkano Says:

    Engineer guy… your wife and children are very lucky to have you :)

    Posted on April 8th, 2011 at 10:04 am

  8. engineerguyvideo Says:

    @cyanidesan Thx for your nice comment … I do keep annotations useful, but it would be nice if I didn’t make errors and didn’t need them!

    Posted on April 8th, 2011 at 10:18 am

  9. cyanidesan Says:

    the only yt videos where the annotations are actually useful instead of annoying.. thanks for keeping it that way Bill! :)

    Posted on April 8th, 2011 at 10:32 am

  10. engineerguyvideo Says:

    @bruderda Transistor is one of my favorite … then next few videos will focus on parts of the computer: The LCD screen, hard drive and so on. This might interest you too.

    Posted on April 8th, 2011 at 11:31 am

  11. bruderda Says:

    @engineerguyvideo Yeah that does make sense! Thanks. BTW I really like the transistor video and will probably watch more.

    Posted on April 8th, 2011 at 12:10 pm

  12. engineerguyvideo Says:

    @bruderda Yeah … the battery is divided between powering the electrodes where the ionization occurs and driving the mosfet section. Not sure exactly how it is divided so I divided it in half. Would have made more sense if I’d showed the single 9V and then added in a voltage divider, but I thought there was enough elements in the “simplied” circuit and so just showed two “4.5 volt” batteries. Does that make sense?

    Posted on April 8th, 2011 at 12:24 pm

  13. bruderda Says:

    You say “9 volt battery” but then show “~4.5 volts” in the diagram at 2:53

    Posted on April 8th, 2011 at 1:19 pm

  14. engineerguyvideo Says:

    @jodex96 Indeed, which makes the MOSFET more amazing. Yet first MOSFET was 1925 (I erred above) by Julius Edgar Lilienfeld. Transistors, of course, grew out of vacuum tubes which could often do the same things – although not as reliable, not miniature, not cheap to make. Check of the wiki page on Lilienfeld .. fascinating reading. BTW The notion of invention is more murky than most people think … historians of technology prefer to tell the complete context, rather than isolate.

    Posted on April 8th, 2011 at 2:19 pm

  15. jodex96 Says:

    @engineerguyvideo Wasn’t the first transistor invented in 1947?

    Posted on April 8th, 2011 at 2:43 pm

  16. Kriskke Says:

    Can you explain why the batteries in the smoke detectors always die in the middle of the night?

    Posted on April 8th, 2011 at 3:26 pm

  17. balls2balls Says:

    Always get a kick out of your videos, Bill. Thanks a lot.

    Posted on April 8th, 2011 at 4:08 pm

  18. engineerguyvideo Says:

    @fswah6 This is a good idea. The MOSFET has a fascinating history the first one was patented in the ealry 1930s .. I believe 1933! They didn’t have technology to really make it … I made a note to look back into this.

    Posted on April 8th, 2011 at 4:47 pm

  19. fswah6 Says:

    @jr52990

    Actually, Bill Nye is a Mechanical Engineer

    Posted on April 8th, 2011 at 5:36 pm

  20. fswah6 Says:

    I think in your video on Silicon you should incorporate the differences between BJTs and MOSFETs and why the advent of the MOSFET fueled the Microelectronic revolution

    Posted on April 8th, 2011 at 6:01 pm

  21. engineerguyvideo Says:

    @GetTheGurus I added annotation to the video. Thx again, much appreciated.

    Posted on April 8th, 2011 at 6:29 pm

Leave a Reply