S2U2 (there are others, its just the one I use) is one of those "slide to unlock" lockers.
When the phone wakes up for any reason, S2U2 shows a lock screen - all buttons are disabled (or you can have the dpad enabled) - you must then swipe a slider across the touch screen with your finger or stylus (or press dpad right for a second or so) to unlock the screen & buttons. Just like the iphone/ipod touch. Hence "slide to unlock."
The practical effect is, if the phone wakes up in your pocket, *and* somehow the slide action happens, you might want to take a close look at whatever is living in your pocket
