This is a follow up to the smoke alarm posting from last week. Smoke alarms do have a requirement for being 4” down from the ceiling, but only when two kinds of ceilings are encountered. Sloped and peaked ceilings have a 4” requirement to the top of the smoke alarm. See the picture below. But on a flat ceiling the top of the detector can be mount right up against the ceiling.
Till next time be safe work safe
Jake