This is how I waterproof my X10 palmpads. This works great for the pool, hot tub, shower etc.
You're probably wondering why I want one of these in the shower. There is a lot of stuff you can control while in the shower. Music volume, track, have your house read you the news headlines etc. (I do all of this with Homeseer)
You could easily use this method to make a waterproof or sand / dirt proof bag for any occasion. It's inexpensive enough you can make a bunch.
It also floats!
Step 1: Cut plastic down to size.
This plastic is the kind you would usually use to cover a table. I purchased it at Walmart, it's very inexpensive. They make it in a couple different thicknesses, I think the thinner stuff works just fine.
I used 8" x 8" squares to start for this bag, you could get away with 8"x7" for the X10 palmpad, but it makes the last part a little harder.
You can adjust the size depending on what gadget you are trying to seal up.