[HH] CO detectors self-destruct

[Tom Metro]

Greg Rundlett wrote:
> I bought a house 6 years ago, and I was perplexed this week as ALL the
> First Alert combo smoke + CO detectors started chirping and went bad. 
> The First Alert smoke detectors have and "End of Life" feature...

As Federico pointed out, this is due to the limited lifespan of the sensor.


> ...you should AVOID any detector that is UL 2034 certified (if possible?)

Every consumer CO detector I've see has a similar limitation. Only the
duration varies.


>  ...ALL the...detectors started chirping...

Perhaps a case to be made for staggering your purchases and/or
model/vendor of your detectors.

The units typically say that once they've reached EOL (end of life) they
cease detecting, so if they all hit EOL at the same time, you're without
any protection.


> Does anyone have knowledge of hacking on smoke detectors?  Not that I
> have time or skill to actually hack on IC if it were possible, I'm just
> curious.

To what end? It's a relatively low cost life safety device. The only
reasonable hacking is to scavenge reusable parts from an expired
detector, like the LCD, alarm, etc. The sensor could be used for hobby
applications.


> Since my detectors were warranted for 5 years, the self-destruct timer
> was set for 6 years.

Ideally, you'd like the two time-spans to match.

Back when consumer CO detectors were first introduced, I had a First
Alert AC powered unit with an LED display. I don't believe it
implemented an EOL in the electronics, but warned of that in the
documentation.

I've since used several of the Kidde KN-COPP-B[1] models, as they've
were highly reviewed. As CO detectors can react to both high levels of
CO for short durations, or low levels for a long duration, I like a
design with an LCD display.

Unfortunately I've seen at least 2 of these units fail with gibberish
showing on the display. I have one in front of me now that shows a faded
"8" in the center digit, and the top and upper left segment of the right
digit fully turned on (not a valid number or letter).

The unit otherwise seems to function normally and passes its self-test.
It is not showing the "END" that is is supposed to show at EOL. The
thing is, it should be. This unit was purchased in December 2009,
presumably deployed that month, and according to the label on the back,
has a 7 year EOL.

I also have a Kidde KN-COB-B[2] (looks identical without the LCD), that
is about 6 months older, and it too behaves normally and has not
produced the EOL chirps.

(I could do an actual functional test. If you read through the Amazon
reviews on some of the most popular models, there's a guy that describes
the testing procedure he uses. But these units are old and in need of
replacement anyway.)

Between the failed EOL and displays, I have less confidence in Kidde
branded units. These units are beyond their 5-year warranty.

To replace them I'm trying out the First Alert CO710[3], which has an
LCD (it displays the temperature when idle, but will show the peak CO
PPM measure in the last 24-hours at the press of a button, and will show
CO PPM when triggered), comes with a 10-year battery, 10-year sensor
EOL, *and* a 10-year warranty. So you've got a decent chance of getting
a full 10 years out of it. But they're expensive...selling for $50 at
Lowes. I found it for $41 at Amazon, and then for some reason a 10% off
coupon offer on the page.

I see today the base price has dropped to $34, and the coupon is still
there for further discount, which seems quite good. Now the problem is
if I get a few more, I'll end up like Greg having all units from the
same vendor expiring at the same time. I suppose I could always delay
activating subsequent units by a month.

I like the idea of having the fancier model with the LCD located near
actual potential sources of CO, like a furnace. (The First Alert
instructions say to place the detector no closer than 20 feet from a
furnace or other combustion appliance.) I'm fine with other detectors in
low probability areas being simple alarms. So I'd like to identify a
lower-end model for those areas. Perhaps the Kidde KN-COB-B-LPM[4],
which sells for about $16. Dare I trust Kidde again? (Physically, the
design has no resemblance to the models I've used, so the electronics
could be completely different.)


I'm not a fan of combined smoke and CO detectors, as the smoke detectors
have a much longer sensor life span. The optical detectors are
essentially infinite (if you keep them clean), and I have ionizing
detectors that are 30 years old that still work (tested with actual
stimulus, not the test button). But of course probably of failure goes
up with age, so anything over 10 years I'd move to "bonus" detection
areas to increase coverage. (I tend to have multiple smoke detector
types distributed around the house, with multiple detectors in some
areas. Primary detectors are optical + heat rise in most locations, heat
rise only for kitchen and garage, and all connected to a central alarm.)


Federico Lucifredi wrote:
> These decaying home versions… I could not
> find out which they are. 
> Does anyone know?

I do not, but interesting question.

The teardown[5] you linked to says the sensor "makes a sloshing sound
when I shake it." And indeed I believe I also hear a sloshing sound when
I shake a Kidde KN-COPP-B and the First Alert CO710.


> ...these detectors cost $25-50 because they have a
> government-guaranteed demand curve, and vendors are just waiting for
> the money to come in.

It would appear that $15 is more like the bottom end, and I don't think
they're squeezing out much profit there. Go up from that and you are
adding convenience (10-year battery, or multiple power sources),
features (LCD display), or warranty. That doesn't seem unreasonable.

I agree with Ethan that the bill of materials for a flood detector is a
lot simpler than a CO detector. Plus, unlike the flood detector, a human
safety device is going to have substantially higher testing costs and
liability insurance. It wouldn't surprise me if that adds $5 to the unit
cost.


> I have all of the above already but not the explosive gas alarm (I
> am a sensor guy, I get these even when I don’t need them to learn more
> about them), do you have a model you use/recommend?

The one in that teardown was a "combination CO and explosive gas
detector" by Kidde, model #KN-COEG-3. Though given his opening paragraph
was about it triggering false alarms, probably not recommended, even if
it is still available (apparently it is; $50 at Amazon[6]).

 -Tom


1. https://www.amazon.com/dp/B0007ZYU7C
2. https://www.amazon.com/dp/B00F99TH10/
3. https://www.amazon.com/gp/product/B011O2WW1C/
4. https://www.amazon.com/dp/B004Y6V6K4/
5. http://www.robotroom.com/Inside-Carbon-Monoxide-Detector.html
6. https://www.amazon.com/dp/B0002EVNJ6