(Makeh B'patish-מכה בפטיש Ep. 45) (#923) Is one allowed to knock on the door with the key, knock on the window, use an electric bell, and have a little bell ring when one opens the door?

Various Examples of What to Be Careful With When Water Flows onto Grass or Plants;

Important Things to Look Out for or to Be Aware of When Going to a Hotel for Shabbos. Public Places Which Have Automatic Doors;

putting down items on the ground in a slippery area. Raising and lowering a chair, fan, etc. Putting down sand in a slippery area;