Slide to unlock has a physical analog, I use all the time on gates and doors. Slide to unlock/lock is OBVIOUS because it is a logical extension of a physical object. IT would be like patenting "Push to open" or flick up to turn on, flick down to turn off (light switch) or any number of common tasks we do in the physical world.
The problem is, people get STUPID when they see "on a computer". It is like they can't function without being hand held the whole time the moment they sit in front of one. I can't tell you how many times "my monitor isn't working" is simply they never pressed the power button. GAHHHHHHHH