This is going to get messy. Really messy. Apple's been granted a patent on slide to unlock. You know what uses slide to unlock? Just about every other touchscreen UI out there, in one way or another. 9to5Mac reports on the patent, which was applied for well before the launch of the original iPhone; that's pre-glacial in smartphone terms. The patent — US Patent 7657849 to be specific — is for "Unlocking a device by performing gestures on an unlock image" and the abstract reads as follows
A device with a touch-sensitive display may be unlocked via gestures performed on the touch-sensitive display. The device is unlocked if contact with the display corresponds to a predefined gesture for unlocking the device. The device displays one or more unlock images with respect to which the predefined gesture is to be performed in order to unlock the device. The performance of the predefined gesture with respect to the unlock image may include moving the unlock image to a predefined location and/or moving the unlock image along a predefined path. The device may also display visual cues of the predefined gesture on the touch screen to remind a user of the gesture.