During some renovations I have opened up enough wall for the inspector to note that smoke/CO detectors need to be hardwired throughout the house.
It is much more convenient to power them using the individual circuits I have created than to try to use a whole new circuit and snake it through multiple levels of the house. The detectors are all wirelessly interconnectable, so they do not need to be on one wire.
As far as the local code concerned, this is allowable. (907.2.11.5 Interconnection - Physical interconnection of smoke alarms shall not be required where listed wireless alarms are installed and all alarms sound upon activation of one alarm)
The question: All the circuits I plan to branch the individual alarms out of are 20amp, 12/2 wired circuits. I was planning on using 14/2 wire coming out of those, going solely to one smoke/CO detector. I know that mixing/downsizing gauges in a branch is typically a no-go, but it seems like this isn't hitting the issues one typically has doing so. Any commentary, especially regarding NEC 2017/2020 code sections prohibiting this specific scenario would be much appreciated.