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

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Michael Dwyer 4d ago

@moira
I doubt this is you, but the networked ones at my moms house set themselves off because they were setting themselves on fire. !

They were AC powered and had a big multi-watt resistor on the board. This heated up enough to blacken itself and set themselves off one after another over the period of a few years.

They were of an age to be replaced anyway, but it certainly rattled my opinion of smoke detectors.

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Solarbird

@mdwyer I've opened several, once Kidde declined to honour their warranties. I've found some bad solder joints, some improperly-applied wax as conformal coating (which also didn't cover the entire intended area), and so on - but ever anything like that. So.