Contractors and inspectors still call and ask about the location of smoke alarms, they want to make sure that the location they put it in is OK.
As shown above it is OK to mount a smoke alarm right up against the ceiling on the wall, there’s no longer that space of 4” down from the ceiling or 4”
away from the corner on the ceiling. The space 12” down from the ceiling is to the top of the detector. This changed in the 2010 NFPA 72. Hope this helps.
Till next time be safe and work safe