To fix the ceiling, it is best to clean the front support from sticking. I did not, believing the ceiling (acrylic paint) clean enough, and the detector was detached after 20 minutes. After cleaning the paint with soap and drying, the support was reattached easily. Colle finally even after s' be lifted once. Hold 15-20 seconds still supported before use. I fixed another detector on an old wooden beam. No worries since purchase.