Inside a proper optical smoke detector (Status) 

Very old design, the IC itself dates back to your very early CMOS process, which was one of the first uses for low power CMOS in consumer electronics, as the battery lifetime with the CMOS IC was equal to shelf life on them. That IC has been around since the 1970's, originally from RCA, but second sourced from many other manufacturers as well. The RCA datasheet for this IC goes into much more detail, including the photos of the actual die itself.

Most entertaining. I can tell that you spent quite a long time determining how it works with this one. I Appreciate the time and effort that you put in Clive.

5:17 These "dark rooms" attracts also small bugs, i have experienced it a few times that one of my smoke detectors starts whining for no reason, while the battery was new. After removing them from the ceiling they stay quiet for a while, sometimes they start again after a short periode of time. The last time i suspected that it was a bug, i placed the smoke detector inside a zip lock bag for a half hour, and the little bug left the crime scene and was visible in the bag 🤣

I recently had smoke alarm give regular false alarms, and when I opened it found out a small spider had moved into the detection chamber. After evicting the spider and cleaning the cobs out it worked fine again. nice teardown :)

The design of the ir lamp and ir detector chamber was very neat, allowing smoke to enter but reducing the chance of outside light to virtually nill, even the screening from the ir lamp was in the same style as the outer ring. Very informative once again Clive, thank you.

I don’t have a lot of electrical engineering knowledge but I feel most of what I have comes from you! As a kid I loved to disassemble old telephones and such just to see what was in it and these video’s scratch a nostalgic itch for which I want to say thanks!

The detector diode is reverse biased and only draws current when illuminated. I think the strobe connection is grounded during the test period so the sensitivity pot works. If it is open (transistor off) the remainder of the the time there will be no current trough the sensitivity adjust resistors. This will conserve battery life as you stated. I think the detector amplifier is a transimpedance amplifier with the input node near V+.. C1, C2, and R14 are most likely loop stability compensation. The most interesting part to me was about the three terminal piezoelectric sounder and feedback driver. I had never looked in detail at one of those. I learned something new from this video. Thank you.

There's an issue with having the piezo sounder standalone in one half of the clamshell; in an 'infapower' CO detector i have seen electrolytic corrosion set up between the sounder and the spring loaded contacts.....the alarm knew it had a problem but couldn't alert me to it since it's voice had gone. Just happened to notice the yellow 'fault' light flashing as i was dropping off to sleep, then found the fault. This was after 6 years into it's expected 10 year life, and it wasn't even in a hostile environment. I won't be using any alarms without hard-wired sounders in future.

I love your reverse engineering of the seemingly most basic electronics...I find them so interesting and entertaining and often feel like I'm learning stuff! But don't tell anybody else okay? 😂👍🏽. Keep em coming!

We have on multiple occasions spiders crawl into the chamber setting them off. My daughter really loves it. Also in my days of theatre work we would have to call our alarm company to have the system put into test if we were running fog or diffusion machines.

Fascinating take-down. I've never been a fan of optical smoke detectors, due to my experience of them in the cable tunnels in the power station at which I spent most of my career. There was a mixture of ionisation and optical detectors due to the different smoke particles that could be expected in a fire, but during every harvest season, the thripps (thunderbugs or corn flies) would leave the fields and head straight for the optical sensors putting them into alarm. The only remedy was a massive program of insecticide spray, carried out either by our staff or the fire alarm contractors.

Some of the modern ones are made around MSP430 microcontrollers rather than that ASSP. The shield is necessary (or at least desirable) because of the small analog voltages in play. The piezo is glued in because it needs to make an airtight seal - there is a resonant chamber there. In the ones I worked on, the piezo was glued to a polystyrene speaker cone that was itself glued to the end of the cavity.

Fascinating to see exactly how the self test works. Thanks for sharing this one Clive.

Interesting Stuff!.. I had a rough idea how the optical smoke alarms worked, great to see it explained by the boss 🤩

My Mum's smoke alarms get tested every Sunday when she makes Bacon Butties.

Thanks Clive, I'm enjoying these videos and your soothing voice while stuck at home with head and muscle aches from my booster vaccine.

Even being a fireman for a few years I never knew exactly how these worked. Thanks for sharing!

Thanks Clive. Really enjoyed seeing that.

Fascinating! It's interesting to see how this stuff works. Although I have to tell you that I needed some kind of smoke alarm that I could silence remotely as I am a wheelchair user and I had some things that were desirable and things I needed from one. There's slim pickings for smoke detectors that met my requirements. The only one I found suitable was the Nest Protect Carbon Monoxide and Smoke detector. The main thing of a smoke detector I needed was for it to be a smoke detector, as in not have any "smart" functionality that would affect it's performance as a safety device. These have smart functionality but that is all secondary to it's primary function. The smart functionality if it can't work, it won't not sound the alarm. The remote "silence" feature is quite good in how it works, it only works via Bluetooth and you have to be in the vicinity of your detector (so you can't silence it from outside, if you could though my partner said that'd make a good murder plot on a CSI xD). There's two types, mains and battery. The mains one has 3 lithium AA batteries as backup and is hooked into the grid and the battery one has 6 lithium AA batteries. They both have a path finding light at night, but the battery one only comes on when it detects a human. It also reads out in clear English which room has the fire or CO and tells you what to do - Great for kids or people that get easily confused. I also like when you turn the light off at night, if all it's self checks have passed, it will glow green for a second, if not it'll glow amber. It also does a test of everything every month (sounder, batteries, connection, link to the others) and they also link to each other as well. They're not cheap at about £80 each, but I'm kinda glad there's not a bunch of manufacturers making woefully inadequate safety devices, but being a wheelchair user I can't reach up and silence a traditional alarm, so after much research, I went with the nest protects as they're sensibly designed and pass all appropriate legislation, and owned by Google they're pretty good with warranties and supporting their product. There's also another 'best effort' feature if you have a Nest Thermostat linked to your boiler. If it detects CO it will try and shutdown the boiler, but whether or not this is effective doesn't matter, you still would have to leave the home, it would just mean the emergency services could enter the property earlier if it was able to shutdown the boiler.

I installed a few infrared laser laser smoke detector in a Temple .the laser shot across the vaulted ceiling ,bounced of a prismatic reflector and back into the unit .it used a visible red laser to help you align the unit ..It worked quite well .No false alarms .Unit came with a bypass key when they would be using incense or indoor fireworks .It was a Chubb Edwards addressable system.basically anything interfering with the beam over a certain period of time would trigger an alarm.Same principles

Absolutely brilliant Clive

Interesting, just last week I modified one of my smoke detectors (out of pure interest I provided it with a 433MHz transmitter) and it works with an MC145012 chip, which is more or less the same as the MV145011 (exactly the same pin assignment, etc. .). The story with the piezo-beeper and the 3 connections still was a mystery to me ..until I came across your video - thank you very much for that :) Regardless of that and said with all due respect: I know that you love to deal with all this Chinese-LED-etc-rubbish-junk and to take everything apart down to the last detail - you do it with the highest precision and with skill, but sometimes I would really love to see you dealing with more "serious", useful (and far more interesting) stuff like - for example- this ...just sayin' .)

Many US states that unit would be illegal to install these days. Most have laws stating any new buildings have to have hardwired units with 10 year sealed battery back-up. So you activate the unit, plug it in and in 10 years it will start chirping to alert you that you need to replace it. Kidde has a list of the laws on their web site for those interested. This is the NY version - Smoke alarms are required in all residential dwellings (single family homes, multifamily homes, hotels, rental properties, dormitories, etc.). Smoke alarms in newly constructed or renovated dwellings are required to be hardwired with a battery back-up, interconnected, and UL-listed. Sales of battery-powered smoke alarms are restricted to alarms with a 10-year sealed battery.

2:19 Yes... I personally prefer when components are spiritually glued.🙃 Thanks for the video! Oh, and really good advice too.

Good vid BC, I have fitted hundreds of these things in people's houses years ago, I honestly never really knew how they worked. 👍👍👍

I have always wondered how these work.... not I know a bit more on the functions of smoke detectors. Thanks Clive!

Fascinating, as always.

A great explanation of the circuitry and how a smoke detector works. Plus, the added info about how important it is to keep the dust trap chamber clean. Also, to press the test button on your regular testing day, e.g. Monday... If it is too high for you to reach, then use a long brush shaft or what you can to press the tester button to check the alarm. Please remember to never cover up or remove a smoke alarm unless it is faulty. Contact your building fire officer and/or handyman. If in doubt about its working condition telephone your local fire station on their non urgent directory number to inspect the alarm. In the meantime, if you smell smoke, see smoke or the alarm sounds, Get Out & Stay Out. Never go looking for the cause or tackle on your own. Use any anti fire Blankets, Sand Buckets, Fire Hoses or Extinguishers etc to aide your escape. They are best used for that purpose to save your life. Leave the Fire Fighting to the professionals who are qualified to tackle a blaze of any size, small or large.

Just what I wanted to learn, thanks again sir

Had a smoke detector go off recently, probably three years old. Cleaned it with a vacuum, but it gave another false alarm a week later. I then blew it out with compressed air and it's been silent ever since, so I guess it's either repaired or completely buggered up :)

Finally understand why these annoying levers are in the battery bay! THANKS!!!

Very interesting breakdown, thank you professor.

Nifty. Learnt that non-radioactive smoke detectors exist *and* that they can be set off by little moist bug feet (Love the myriad ways you turn a phrase). A day that you learn something new is a day that hasn't been wasted.

I recently bought a new smoke alarm and thought everything was okay because it regularly blinked it's little LED. But when I tested it again, after about 2 weeks, it just turned off with a low battery instead of beeping 🤦‍♂️ I guess this is why many smoke alarms are hard wired now days. Test regularly.

See, now I want to build a gazebo in the style of that smoke detection chamber. All the breeze and none of the sun in the summer?? Sign me up! 👍

Also if you want an Australian Smoke detector I can send one over. AMPAC have a detector that gets its loop address from switches on the detector that are actuated by fingers on the base. Which means of you replace a detector in the same base it always gets the same address. Most of the other makers program the address with software or dip switches on the detector. Fire detection loops are quite interesting. Tyco another Australian manufacturer actually provides a lot of technical detail on how their loop works. Voltages, currents and signalling etc.

It's good a lot of clever circuitry in it

YAY, now can see what is salvageable from old ones.

The way they use the Schlieren effect to see the particles is also incredibly impressive considering the simple design of the chamber.

The periodic Illuminate-Check cycle and rechecks looking for an increase in reflectivity will also avoid false trips from things like strobes that are bright enough to get into the chamber.

The only ones they carry at the local hardware store now don't have a replaceable battery. It allegedly lasts ten years, then you have to replace the whole thing.

I have installed about 50 ei electronics ei650 smoke alarms in my life. They are excellently made and have a 10 year battery. The cost is perfectly reasonable since you pay for 10 years and you really are getting much better quality than with your average smoke alarm. They can also transmit diagnostic data to a smartphone via the beeper.

Thanks BigClive I have just tested and replaced the battery of my smoke detectors

Rare to see optical smoke detectors today. Most are ionization. I have a 1970s AC-Powered _Vanguard 'Smokesonic'_ which uses an incandescent bulb as the light source. Strange looking gold perforated metal "bell gong" style device.

I recently took down fire detectors that had no electronics from an old house I bought to remodel. Very heavy and took me some time to figure out all the gizmos that made it work, when it turned out to be quite simple, yet effective if you were within earshot. I would love to send you one if interested. Ear plugs are a must. You might already be familiar with them. They are quite heavy.

I saw the video announcement and immediately had vision of “The Mask” with Jim Carrey saying “Smokin’!” Great tear down thus far Clive!

WIth the new regs in Scotland the costs are increased significantly. Whilst looking for a new system to meet the regs I noticed that you could get either mains powered interlinked detectors or battery powered linked detectors. but they are no compatible. In my house the main living accommodation is on the first floor meaning it would have been easy to install mains powered detector but down stairs would have meant damaging ceilings and the need to fully decorate etc. Its a shame that there isn't a hybrid system that allows both battery and mains powered devices to be interlinked. That said the FireAngel detectors I have installed work great.

The way the face of that sounder looks, looks exactly like my plasma disk

There's so much going on. Cheers for the tear down and explanation. I would like to see a tear down of the singing bear you showed on the live stream a couple of weeks ago. :)

Oh I "love" playing the multiple reattaching clips game! Especially on large, cumbersome objects like tower fans 🙄

Remember that smoke alarms have a sounder and smoke detectors just detect air contamination and have a seperate device to sound the alarm. I've come across many fire industry people who incorrectly use these terms interchangeably.

Reminds me that I need to replace mine. Thanks for this

My personal favorite is the Fireangel Angeleye smoke detector. It just screams quality, at a decent price. Might wanna take a look at them, Clive.

The Spider comment is interesting Clive, the one in our bedroom went off at 6:30 am the other morning for a few seconds, not a beep from it since ... maybe I had a wayward bug too !

Nice demonstration you made here, so now we need to look inside one of these radioactive ones which charges the smoke particles when the radiation strikes them and generates a voltage on the sensor, nah I know you already know this and I value your safety. keep up the good work!

感謝你拆偵煙式住宅用火災警報器研究 非常有用

My old boss thought he had a gheko in his light fitting. Took about a week of cool winter nights to work out it was the occasional low battery chirp of the smoke alarm as the battery finally reached ambient temperatureand lowest voltage late at night. Next year all rentals in Queensland Australia require hard wired or wireless interconnected smoke alarms, so if one goes off the rest will. Thanks to lithium cells, the wireless ones have a 10 year battery life. That optical detector is just brilliant except for the occasional bug detection.

Last time I went to buy a battery for a smoke detector, I discovered that a whole new smoke detector of exactly the same style with 9V battery included was around the cost of a premium brand 9V battery (about $5). I replaced the whole thing and threw the old one in the electronic scraps bin.

Good advice about changing them out every ten years. I'm still using ones that were installed twenty years ago which is probably a really bad idea...

Would like to see a breakdown of an aico Ei 3028 multi sensor and Ei3024 heat and CO.

Seems well designed, and this one's not radioactive! I personally find status products to be quite good.

I wonder if those screws with tape over them are just to show if you happened to tamper with the alarm.

Thank you Clive

Clive, Great video as usual - you always have the best reviews. Concerning this circuit and the MC145011 chip and supporting circuit, it would be interesting and possibly useful to hack the circuit and make a real air and particle detector. You could take the signal off from the IR receiver and count the number of particles as air is driven through a small chamber. This could be so much easier to deploy than the multi-thousand dollar instruments currently used to detect air pollution and contaminants suspended in the air. What do you think of this approach?

Great video, as always! Would be great if you would do one on the various bms boards available on Aliexpress, such as the HW-391 bms. I've seen them used in upgrading power tool batteries from NiMH to Li-ion, and I wonder how reliable they are. Thanks for all the work you put into your videos.

Regularly replacing them seems like a good idea. Though the really good combined smoke and heat detectors are quite a more expensive and if you want them in a non-fugly design with useful features like low volume testing (and yes, it's important to make sure they actually do work and can make a sound) or mesh networking then they're *way* more expensive than the regular cheap ones. Mine (without networking!) cost around 45€ a pop and I have 9 of them in my home...

Awesome big Clive

They usually have a manufacturing date, a spot for an installation date, and an expiration date on the label of most smoke detectors. All of mine were expired after 10 years.

Informative and interesting and maybe saving lives one video at a time. ⚡️⚡️⚡️🍻

Learned some, left happy ;)

timely...i just pulled one apart the other night as it started going off at 3am for no reason whatsoever (it was only tested by licenced electrician/installer like a month ago..SMH)...this one has a pack of 3 cr2023 button cells on a little board with some passives (rechargeable) and its wired into the light circuit, and to a 2nd alarm in another room... it also didnt have a peizo, it has an actual speaker like from an old phone handset... i didnt pull the chamber apart, but it looked very much the same from the outside i put it all back together and put it back in place, did a test n it worked, and havent had an issue with it since.. i think the batteries where not charging correctly as the voltage was less that 1v (altho it was still loud as hell n woke me up...twice!)..im thinking the electrician may not have placed it back on its holder correctly and the mains connector pins werent making a good connection or somthing

I starting to think Clive might be the reason we are having supply chain issues. His Fleabay shopping sprees surely have to take up a few ships that would congest even the largest of ports... Thanks for the great content.

I use both ionizing and optical smoke detectors, one is good for flash fires and the other for smouldering fires. To clean the optical ones I use compressed air after vacuuming. My problem is getting to one that is at the top of a 20 foot ceiling, short of erecting scaffolds in the living room I can't get to it. Very interesting on the design and power saving choices made.

Hey, I love your explanations. Can you do a teardown of an in grund invisible dog fence, and how viable is to extend its range (cable range) I've seen them in aliexpress for around 30 quid

Awesome video might I suggest a teardown of an ionization smoke detector

So many of the tv news reports about fires mention smoke detetors that weren't working properly, or which didn't have batteries installed. One solution to this is the newer units that have come out that instead of the typical 9V battery has a built-in lithium cell of some sort. Designed to last "the life of the device" and then the whole thing gets replaced. I know of at least one locale where these are mandatory for rental properties.

Going deeper with Clive. Good channel name.

As always, an excellent and fascinating analysis, Clive. Perhaps proper conformal coating would be more suitable to coat the sensitive receiver electronics. Though, it is still altering it as you say. People must bear in mind, the real cost difference between a correctly engineered smoke detector and a fake, is your life. Don't skimp on it.

I opend some smoke detectors produced between 2001 and 2020 (sold in Germany); all chips: MC145012, A5358 and CS2105GO-M12 are fully pin-compatible and use the exact same circuitry

Thank you, very interesting and entertaining indeed! A problem I have with smoke detectors is that the low battery warning always occurs in the middle of a cold winter night. Our room temperature (thermostat) goes lower at night which causes the detector battery voltage to sag enough to trigger the low battery beep. I easily sleep through some random beeps, but unfortunately my other half does not and forces me upp to resolve it at once. I tried NiMh batteries that I charged every year but they didn’t last much longer than a good disposable battery. Maybe a smoke detector that runs on two (rechargeable) AA batteries with low self discharge could work longer/better?

i made an electronic tuner sensor from the piezo crystal, good for acoustic guitar, clamped on from a capo. no clip on tuners back in the day. piezo good for el cheapo pickup taped to an acoustic guitar too. yes we live and learn dont we?

Now we need a smoke detector testing set up next to the 2 fork cooking chamber. How many watts does a sausage need to activate a smoke alarm?

We here in New York USA now have to buy smoke detectors with built in batters. No more replacing the battery. Just thru the unit away.

I had a few false alarms with cheaper smoke detectors and at some point got fed up and bought rather expensive EI Electronics ones. These are great, 10 years claimed battery life (around 6 years old now and tests fine still) and seem to be really well made (nice double sided PCB with good soldering quality). Not made in China, too.

Since it a safe device, the three connections in the piezo maybe are used to periodically test if the speak is working using some inaudible signal.

Nice a video on smoke detector as ever going to be interesting

I find it fascinating that hanging a few 10 pound devices on the ceiling here and there will safe your life one day. Just how it detects smoke is soo cheap just a piece of plastic and 2 diodes, yet it's soo reliable.

Thanks for another great video. I wonder if such detectors can be used to detect vaping?

I must reiterate what Clive mentioned. There are some things you don't try to save money on and smoke detectors are among them. I still like the old school ionization base detectors with Americanium inside. They seem to False alarm less, but they are hard to find now.

Worth watching just for the spider impersonation alone 🕷️

I recently got rid of all my cheap smoke detectors and went to all wired detectors with battery backup and if one goes off it will trigger them all...I also get a notification on my phone. They were expensive and I had to have a electrician install the mounting plates but I saved a ton on my home insurance and I no longer worry as much with my 8 day prints on some of my 3D printers...

I have a GMRS radio antenna in the attic above one of my detectors. When I transmit at 15 watts the detector chirps.

2:36 I was really hoping for the 'we must go deeper' reference :D

My guess would be that they have some sort of smoke analogue 9replaceable chamber top) and then adjust the set on test resistors to give the correct output level.

Good Friday morning to you sir

i've had mine for 7 years, maybe time to look into a new one

The property manager has someone come out to test the smoke alarm every year (I think it's required by law for units/flats/apartments/MDUs). They replace them every two to three years too. You can tell the professionals, they're the ones with the can of smoke rather than the ones with a stick they use to poke the test button. Occasionally they replace the battery, but most of the time they just leave it up to the tenant. They are getting better though, we've had smoke alarms in the stairwells pinging for months before they could be bothered to do anything about them. Doesn't bother me though, since I sleep with earplugs for the road noise anyway.

would you care to take a look at the philips ultra efficient bulbs? from the looks of it they are the dubai lamp without the dubai lamp branding. but they do share basically the same efficency.

i have a spot for mains live version of these. original one sat there buzzing away turns out last person lived here messed with it and cut wires. past 4 years found out hard way just never worked its from the early 80's but its so weird looking, i kept it for a antique piece cause its interesting. then i put a new one in and it failed 3 years before its replacement date and had it barely 2 to 3 years, but on good note the new one to replace the one i replaced of is dual source so it runs ac but if fire ever happened electrical and blew the power the battery will take over as last newerish one did not have a battery backup.

I wonder if the KD marking is for the Kidde brand?