Been there fixing this exact issue for a neighbor last month. Their smoke detector was hanging by one screw and a strip of packing tape, so I just drilled a proper hole and used a toggle bolt to secure it into the drywall. Took ten minutes and saved them from having it fall down at 3am and scaring the cat half to death. Battery powered ones work fine if you mark the change date right on the calendar with a big red circle, but that mounting has to be solid. You ever see one of those detectors come loose and start false alarming every time the furnace kicks on?