On Friday, 19 July 2019 14:16:04 UTC+1, Chris Green wrote:
"Most houses ..." seems a little hopeful! :-) I think in reality very
few houses even have interlinked smoke detectors

I'm sure people here have above the average number of interlinked smoke detectors.

and there isn't a requirement for interlinked (wired or radio) alarms
to be on the same or dedicated circuit.

wired interlinkeds have to be on the same circuit as otherwise there'd be leakage between different circuits from the voltage on the interconnect wire.

Owain