Any suggestions for a low-profile hardwired Smoke (and Smoke/CO2) detector?  

The most eloquent solution was an in-wall mud around smoke detector mount but at $159-179, a bit steep + it’s certainly something to get the building inspector’s approval of first (SeeLess says they have test data). (Pic attached)

Kidde had a very low-profile unit but it was discontinued. (Pic attached)