Mastodawn

Okay so let's write this down to think it though.

The latest smoke detector to howl pointlessly into the night sends out 11.3V DC onto the signal pin when triggered but running off batteries. I suspect that's 12V nominal, and it probably delivers 12V when operating on AC power.

Most importantly, it's not like... 500mv. Or AC. Or complicated. It's simple DC.

When acting as a non-reporting _satellite_ node, it triggers when _receiving_ 4V DC on the signal pin (4.0 exactly), and that voltage is polarity sensitive. -4V doesn't trigger the alarm.

(1/n)

#electronics #SmokeDetectors #why

Checking for DC on the signal line, I get functionally nothing. 20ma DC at most, and even that's something I'm picking up out of noise floor shift rather than direct measurement.

My _thought_ was that if the signal line was somehow floating in whole number volts (for whatever reason) than maybe somehow the right RF noise could kick it over.

The problem with _that_ is that I can now _also_ confirm that non-detecting units go off _exactly as long_ as a detecting device keeps saying it's detecting by putting voltage on the signal line. If that voltage goes away, so do the satellite alarms - and immediately.

And that's not what happens. We have to manually intervene and shut the alarms off ourselves.

(2/n)

#electronics #SmokeDetectors #why

The reason I paid meaningfully more than baseline for this particular set is that they report exactly which detector went off and why. That way, if it were the signal line somehow triggering the alarms, none of them would claim to be the originating unit; they'd all report it came from the signal backbone.

But they don't. There's always a unit claiming to be the active detector and it's always smoke (and there is *never* actually smoke), and none of them shut up until we shut off that unit, which sometimes seems to require removing it from power.

So today's afternoon check was basically just another way of confirming what we already knew, and I guess I've done that now, but...

(3/n)

#electronics #SmokeDetectors #why

All _that_ does is get us right back to where we started, which is, "we have alarm after alarm after alarm of different makes, methods (ionisation, photodetector), and models which just in this house are determined to go off randomly, usually but not always at night, for absolutely no detectable fucking reason, and then pass self-test just fine afterwards."

And no, regular cleaning - even weekly cleaning - does not help. I do _all the things_. None of it stops the problem.

(4/?)

#electronics #SmokeDetectors #why

If you're new to this adventure, I have heard this exact same story from _many other people_ at this point - though nobody I've talked to has said they've literally taken metres to the signal wires to verify that way.

Regardless, I know it is not just us.

What I've been told from others who deal with this is to RMA individual units that trigger randomly one at a time until you end up with a set that doesn't. And I guess that's what I'm gonna do, but

holy shit, team

holy shit

(5/6)

#electronics #SmokeDetectors #why

this is the opposite of fire safety

this is the opposite of how anything like this should ever work, I mean

what if all the RMAs are getting you are a set that won't go off even when they should?

but whelp

guess i'm gonna find out

'cause this sure ain't workin'.

(6/6 fin)

#electronics #SmokeDetectors #why

Well, the good news is that _unlike_ the makers of the previous smoke detectors we've had who refused to honour their warranties, BRK/FirstAlert gave absolutely no pushback on this. They don't even want the original unit mailed back, they told me I could just toss it out.

(Since it's optical, I can recycle it cleanly.)

#SmokeDetectors

@moira It sounds like your alarms are actually alarming, as if they sensed fire, at night.

There's this info about marginal battery power and colder temps leading to low battery chirping at night.

https://www.kidde.com/support/smoke-alarms/nighttime-alarm-chirps

Could something like that be involved?

I also have had problems with false alarms from a variety of units, models, technologies, and brands. I'd love to have a better solution than the one you outlined.

1/

Why Do Smoke Alarms Always Chirp in the Middle of the Night?

@moira I have stopped buying networked devices that need every device individually silenced and devices that take wired rather than battery power. These are both aimed at making it simpler to find the source of the false alarm and silence it.

I know that having alarms that don't trigger every alarm when one senses fire is slightly more dangerous, but the usability trade-off is terrible.

2/

@david42 Yes, as per thread, one specific unit always reports having detected actual smoke. Not chirping, full alarm, due to smoke detection. Also, I check batteries, and it is _not_ a battery issue regardless.

(Curiously, they never report having detected carbon monoxide.)

Also the reporting unit is not difficult to find as it announces itself, and when between announcements, flashes a reasonably visible red LED. You do have to get close enough to see it, but the offender is reasonably clear.

As for here, networked is a code requirement and we also get an insurance discount for networked alarms.

Rue Mohr 5d ago

@moira ok, Here is my other idea (but it doesn't explain everything either) maybe there is a significant DC voltage difference on the neutral (or reference) line in this building. If these detectors are in stand-alone (network line not connected) does this still happen?)

@RueNahcMohr ...like a -3 or -3.5 DC ground to neutral or something? that would be fucken weird but... it's something I can check I guess... but why would it matter? I mean, reference is reference and ground isn't connected to these alarms, the only reference they have is neutral.

Rue Mohr 5d ago

@moira yea, like bad splice and a load that somehow creates a DC bias (??)

nightmare on an intermittent problem.
what brand you have in right now?

Rue Mohr 5d ago

@moira or, ya know... unregistered random device on the network? between hot and signal? :]

@RueNahcMohr No. I am routinely in the attic, because I have antennas up there, and I know what animal infestations look and sound like in part because we _have_ occasionally had rats in the crawlspace. But this circuit doesn't go there.

Rue Mohr 5d ago

@moira
hmmmm.....

Rue Mohr 5d ago

@moira .......

does your area have shallow bedrock and your house has a deep basement?

@RueNahcMohr Our house is on glacial till. Insofar as we _have_ bedrock, which we do not, it's far, far below. xD We are on relatively _stable_ fill, however - by our standards it's quite firm.

The house is _very_ underground, _sort of_. It's built into the side of a hill. Three and a half storeys (five levels if you count the halves), and in front the bottom level is even with ground, and in back without the giant retaining wall only the _top_ floor would be above ground. _With_ the giant retaining wall, the second-from-top level is 2/3rds above ground in back.

@RueNahcMohr So deep basement: ...sorta?

What else can I talk about? The reason I wanted to confirm how the inter-unit signalling worked is because we have _freakish_ RF around here. Not just us, but us in particular, because that giant retaining wall is kind of a reflecting dish complete with angled in sections at both ends.

Older neighbours tell me that back when garage door signals were simple, garages would just spontaneously open and close. And those are people who don't even have retaining walls.

When I had my little recording studio here too, I ended up having to put RF chokes and filters on _everything plugged in the entire building_ to stop getting KUOW and BBC - both! - audibly on ribbon microphone amplifiers.

@RueNahcMohr BBC World Service - that, I understand. That's easy. But KUOW is _FM_. How did _that_ work without a demodulator? I have _no idea_.

Rue Mohr 5d ago

@moira OOOH, well, ok!

{Rue puts the tinfoil hat on the smoke detector}

@RueNahcMohr Well, I managed to get a measurement for DC offset neutral/ground, and ... nope. Not there. Not on a nearby general-purpose power circuit, and not on the removed detector mount point either, so that's two different circuits. Same 20mV noise and that's all I see.

Which is good to check anyway, I suppose. But, well.

Rue Mohr 5d ago

@moira yep, I'm going to go with the heavy RF as the cause then, feel like foil wrapping your detectors?

@RueNahcMohr I felt silly enough putting RF chokes on the hot supply. YEAH I TRIED THAT xD

Rue Mohr 5d ago

@moira well, I will only briefly put on the tinfoil hat and say "radon", but without immediate bedrock, I dont think so.

@RueNahcMohr oooooh that didn't even occur to me! But yeah, we mostly don't have radon issues around here, because mostly, we can't.

The tradeoff is earthquakes and volcanoes! Cascadia is a very dangerous place to live, over time. xD

@moira I'd check your wiring and see if you can find some weird behaviour or loose wiring or something. I couldn't imagine the why or how but given symptoms perhaps it's the environment and not the alarms.

Also, I'd absolutely give in for a while and switch to battery operated just to have some peace at night.

@cereal_cable I don't think so, because not included in today's writeup is that I've inspected and verified literally every available connection and also replaced literally every harness. While I'm not an electrician, I was an electrician's assistant for a summer in grad school and did read code, so I have a reasonably good idea what it should be like.

(Also, I've done my own electrics - permitted and inspected, of course - recently. The inspectors say my work is still quite good. Don't ask me to touch high voltage tho', I've forgot _all_ that shit xD)

@moira I declare that this must certainly mean you have ghosts.

@cereal_cable where's egon when you really need him