One of the two conditions needed for משקה הבא לאוכל (squeezing liquids onto solids).
using Velcro, zippers, buttons, clips, straight pins, etc. on Shabbos;
Removing Moss and Algae from a Pail, Damp Wood, Rocks, etc.
Is one allowed to knock on the door with the key, knock on the window, use an electric bell, and have a little bell...