passcode lock apps?

I've been doing a search for an app that would replace the generic pass code screen for the iphone. I've looked through the app store, cydia, and google. And as of yet, I have found nothing. Are there any apps out there for this?
I was thinking of something along the lines of having a pattern based pass code entry. Kind of like that latest Bruce Willis movie, where a pattern had to be entered, instead of some numeric sequence.