It was a portable ac unit that has an exhaust hose that connects to a bracket you put in the window. The bracket had no way to be secured to the window and the window on my building is small and doesn't hold much weight on the bracket. So I put 3M double sided tape on the top and bottom of the bracket before I put it down in the groves of the window, then taped the outside of it with aluminum tape. I guess that wasn't enough because it came back out... I am taking two pieces of flat bar that are a little bit longer than the outside of the window and I am going to secure the bracket from the outside so it cannot come out again. Something I should have thought of to start with, and am now kicking the hell out of my self for it.