need help with ceiling mounts

[monocus]

put the stud finder against the ceiling -then turn it on and move it.another way is to put the sensor on metal and hunt for the screws.also try deep scan mode.your joists will be at 16 " centers.if you still dont have any luck,put a tiny drill bit in a drill and drill into the ceiling at 3/4" spacing.any resistance will be your joist and you can patch the tiny holes with a dab of dap caulking