wired smoke alarm from subpanel

Hang another alarm on the same circut to bitch when the power goes out.

Do they ever get connected between the main and the bus bar? In other words no breaker? I'm not suggesting anyone do that. I think mine might be hooked up that way. new house. If it is that way it was done that way for a reason and not on accident. I learned this when I was trying to silence a nuciance alarm (Having some new pipes soldered and kept tripping). I switched off every breaker, one at a time, and the alarm never went off! Switched the main and it DID go off. Strange!

The only piece of equipment I am aware of that comes off before the mains, is a fire pump.

Please send pictures of any wiring you have in the panel that is ahead of the main breaker.

Me thinks you just missed it and then the detector cleared itself. New homes have a battery backup in every detector as well as the 120v power.

My understanding was that they are to be connected to a branch circuit breaker that also feeds lighting or other circuits where if the breaker tripped you'd notice nearly immediately, e.g. kitchen lights, dining room lights, etc.

Note too many breakers are not rated for multiple wires under the ;oad terminal, if this is the case than it implies a junction box will be required somewhere downstream (perhaps adjacent to the breaker panel, perhaps the nearest alarm, etc.) where the alarm feed branches out.

I have seen 120V hardwired detectors w/o as well as w/ battery backup, though clearly the latter is to be preferred, and local code requirements might you to the latter anyway.