The current problem with touch screen password screens is that smudges can give away what your password is if you don’t clean them right after you log in. The smudges reveal where you put your finger to press the numeric touchpad or the pattern you put in.
The simple solution is to randomly change the location of the buttons each time the screen is presented. This only works for numeric touchpad’s though and has the issue of people expecting numbers to be in order. So I recommend using colors instead.
Here are examples of what it would look like:
This would eliminate the issue of smudges giving away passwords making a much more secure way of protecting cell phones.