I was using three of these as door stoppers to prevent my cat from opening the sliding door. Since the three stoppers do not have double-sided tape, you can apply double-sided tape before use. One is unused. Also, two of them have bite marks from the cat, so please check the photos before purchasing. From the purchase site: Easy and safe window stopper that you just stick on with double-sided tape. Can be used to prevent mischief by children and pets, and to prevent falls. Simply stand up the plate to lock. To open and close as usual, leave the plate down. For increased strength, use multiple stoppers. Easy to install with adhesive tape, no drilling or tools required. Strong 3M tape is used for strong adhesion. It can be removed cleanly without leaving marks on furniture. *When removing, please warm the adhesive area with a hairdryer. Can be used not only as a window lock, but also for drawer handles, toilet seat handles, and laptop stands. Made of safe ABS resin plastic material, non-toxic and tasteless, and gentle to babies.