This trick uses simple physics to recover your key if it slips into water. By attaching something that increases buoyancy - like a small sealed air-filled object you can make the key float back up instead of sinking. It works because adding trapped air lowers the overall density, helping it rise to the surface. How well it works depends on how heavy the key is and how much air the attached object can hold. Lighter keys float quickly, while heavier ones may need more buoyancy to lift them.