We know all about the store-bought cases and protectors for mobile devices. We have used and reviewed dozens of them. But maybe you are between cases? Or maybe your case is waterproof but doesn't float? Or maybe you need a way for your guests to safely get their electronics, devices and valuables between the boat and the dock, the boat and the sandbar or just as a general precaution for items stowed in a totebag or windbreaker pocket. In all of these cases, a zipper seal freezer bag and a tennis ball will do the trick as shown. Need more buoyancy? Add another ball. Or blow in the bag to inflate it a little. Just don't overload it. As with a boat, if the load exceeds the displacement a sinking will result.