24x36 is still a window, why would it not have double stud? I mean,
it's not THAT small.
And are you sure you are using the battery powered stud finder
correctly? Read the directions. With mine, you put it on the wall
_first_, then turn it on, then slide it from side to side. And it has
nothing to do with nails either -- it measures the drywall depth using,
well, something akin to sonar I imagine, like the old knock and listen
trick -- and has no problem locating the wood stud directly through
many layers of paint and whatever, nails or no nails. Only problem is
when the wall is bumpy.