Antique hardwired alarm

[John Kogel]

This is in a 1940 house that had Knob + Tube wiring, all upgraded to grounded circuits at the wall receptacles.

I doubt the wiring to this old smoke detector was actually replaced, but it is certainly energized. Is this alarm wired into the keypad by any chance? The 'keypad' takes an actual key. There is a horn in the attic.

I was too chicken to try this - Find a lighter, burn a realtor's biz card under the detector. If I had tested the alarm, how would I have turned it off? Or would it have a timeout for testing?

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[Jim Katen]

I think it's designed to respond to heat, not smoke. If so, there's probably a bimetal element inside that would make contact when it gets hot and break contact when it cools off again. I wouldn't have even thought about testing it.

[John Kogel]

Thanks, Jim. The bimetal heat strip would hold the horn on until it cooled, I imagine. It could very well be in working order, but naturally I called for new alarms everywhere.

I avoid the temptation to test smoke alarms that may be tied into whole house alarm systems.

Ever since the day I triggered an alarm nobody could tell us how to turn off. The lady in the house had never in 9 years reprogrammed the keypad. I clipped a wire to the bell, after 20 minutes of hysteria in the house. No, thanks. []

Question, is 'bimetal' synonymous with 'dielectric'?

[Marc]

Question, is 'bimetal' synonymous with 'dielectric'?

I don't think so. Dielectric refers to the generation of an electromotive force whose magnitude depends on the temperature of a junction of dissimilar metals. Bimetallic refers to a junction of dissimilar metals which mechanically distorts depending on the temperature of that junction.

Marc

[Jim Katen]

. . . Question, is 'bimetal' synonymous with 'dielectric'?

No. Dielectric is what happens when you hold onto the wire too long.