[dcchuck]

Thank you for sharing. I particularly enjoyed the call out where you highlight what you learned from the incident. Took the post from fear-brain to information-brain for me (don't mind my curiosity haha).

I had a much less intrusive incident but equally "alarming" ;). The apartment I live in has hard wired smoke/carbon monoxide alarms (with backup battery). One night, ~2am 1 of them starts beeping that the battery is dead. I confirm the breaker didn't flip or anything...finally decided to complete disassemble it and get some sleep. 4 of these in the apartment. Head hits the pillow and a second one goes off! Take all 4 down and live dangerously for an evening.

In the morning I do my research - turns out these things just start doing that after 10 years. "Get a new one!" it peeps incessantly.

Shame me please - as I bought replacements. I'll save this post for myself in 10 years so at least I can be the one to say "I told you so".

[tialaramex]

Fixed lifetime suggests ionization rather than optical sensor? If so yeah, they have a specific lifetime, it's just physics. There's an Americium-241 source, a tiny, tiny amount of radioctive material in a sensor which is decaying constantly, and once it has decayed a certain amount too bad, buy a new smoke detector.

There are arguments for or against both types, but ultimately "Make sure you replace it every ten years" doesn't feel like a huge problem. If you really can't do that, then the optical sensors don't have this property - they will still need new batteries, but of course you can just swap those out on a schedule when it suits you, they're typically a cheap household 9volt battery (yes even for a mains smoke alarm, fires don't magically stop when the power goes out)

[cowsandmilk]

> Fixed lifetime suggests ionization rather than optical sensor?

Not at all. The 10 year lifetime is something that was set by people concerned by the lifetime of the electronics. The half life of the isotope in smoke detectors allow them to last well beyond 10 years. (The half life is 432.2 years)

[sidewndr46]

I installed some gas sensors like this a while back. It says in the manual that some date after installation they trigger and stay that way permanently.

[oniony]

No, but you'd think they could charge a battery/capacitor during the good times and use that charge during the outage.

[rwky]

10 years, you're lucky, one of mine just started doing it after 4 years, it comes with a 5 year guarantee but of course I don't have the receipt and even if I did I don't have the will to fight for a replacement. I think these new alarms are designed to fail early I've never had one fail before but after checking up on different makes and models they all seem to fail randomly.

[duskwuff]

This is by design, and it's for a good reason. The carbon monoxide sensor chemically degrades over time. Good CO detectors will perform self-tests periodically, and will go into an end-of-life mode when those tests fail, or when the sensor's expected lifetime has expired.

[fallinghawks]

FWIW some smoke alarms have a manufacture date printed on the side, so a receipt might not be necessary.

[mjevans]

I would love the wired ones to just have a built in super capacitor; enough to give it 5-10 min (minimum) runtime during a power outage. No Battery. ONLY alarm loudly for sensor detects possible smoke (known positive detection), very softly for sensor broken (failed self test).

[saaaaaam]

The battery isn’t for incidental power outages. It’s for when a fire starts somewhere in the building while you are asleep and melts some wiring, knocking out the power to the smoke alarm. An hour later you wake up in a house full of smoke and die.

That’s why smoke alarms have batteries.

[bagels]

Two in the same night? I wouldn't have been so quick to dismiss it as "it just happens". Scary.

[Terr_]

Hmmmm, we had two cheap quartz wristwatches with a drift of +/- 15 seconds per month, and they were allowed to run for 5 years, drifting in opposite directions, we might expect a difference between them of 0.5 hours.

So having two of these detectors going wonky with "just" a 4-hour difference doesn't seem too far outside the capabilities of some kind of "replace me" timer circuit.

Obviously it could also be Invisible Evil Gas Traces, and the impact of being wrong is severe, so I wouldn't blithely dismiss the alarms as planned obsolescence either.

[sidewndr46]

same thing happened to me at about 3 am one morning. I'm thinking the house is burning down. Eventually find out there is no fire. Get the ladder, take down the smoke alarm. Go to remove the battery. On the back it says "non replaceable battery, unit can not be serviced". So sledge hammer + trash can it is!

The next day I tell my landlord I destroyed the thing and need a new one. His reply was that I had vandalized his property.