A lock screen is a user interface element used by various operating systems. They regulate immediate access to a device by requiring that the user perform a certain action in order to receive access: such as entering a password, using a certain button combination, or by performing a certain gesture using a device's touchscreen. While most lock functions on PC operating systems only utilize a login screen, lock screens on mobile devices often provide more functionality beyond unlocking the phone: such as notifications for emails and text messages, a date and time display, or shortcuts to certain applications.
Lock screens by platform
Mobile operating systems
Operating systems that run on smartphones and tablets typically use a gesture-based lock-screen. Mobile phones manufactured by Neonode were unlocked by swiping to the right on its touchscreen. Apple's iOS; used by the iPhone and iPad lines, utilizes a similar unlock mechanism using an on-screen slider widget to the right. Beginning on iOS 5, sliding in the other direction sends the user directly to the camera app. On iOS 7, the slider widget was removed as part of a larger overhaul of the iOS interface, and users can now swipe from any point of the screen. The lock screen also displays a clock, notifications, and provides audio playback controls.
At first, Android did not use a gesture-based lock screen, electing to just require the user to press the phone's Menu button. On Android 2.0, a new gesture-based lock screen was introduced, displaying two icons: one for unlocking the phone, and one for setting the volume mode, activated by dragging the relevant icon to the center of the screen on a curve (similarly to a rotary dial). On Android 2.1, the rotary dial was replaced by two tabs on either end of the screen. Android 3.0 introduced a new design: a ball with a padlock icon is dragged to the outside of a circular area. On 4.0, the option to unlock straight to the camera is provided, while 4.1 adds the ability to unlock into a Google Search screen by dragging up. Android 4.2 makes additional changes to the lock screen, allowing users to add widgets to pages accessible on the lock screen by swiping from the left edge of the screen. The camera is accessed in a similar manner by swiping from the right edge of the screen. Android also allows devices to be locked using a password, a pattern on a grid of 9 circles, or with facial recognition.
Android distributions by other manufacturers typically use different lock screen designs than what stock Android utilizes; newer versions of HTC's Sense used a metallic ring dragged from the bottom of the screen to unlock the phone, and also allows users to launch apps by dragging their respective shortcut icon into the ring instead. On recent Samsung devices, the lock screen involves dragging in any direction from any location on the screen (with TouchWiz Nature devices, such as the Galaxy S III and S4, it is also accompanied by a visual effect such as a pond ripple or lens flare); similarly to HTC's lock screen, app shortcuts can be dragged up from the bottom of the screen to unlock directly into them.
PC operating systems
Windows NT has offered the ability for users to "lock" their computers by displaying a login window, which requires that the active user's password be entered to re-gain access to the system. Since Windows XP, the lock function has also been bound to the keyboard shortcut ⊞ Win+L. On Windows 8, the lock screen has been re-designed to closer resemble those used by mobile operating systems; users can choose a distinct wallpaper for use on the lock screen, which now also displays a clock, calendar events, and notifications from other apps. The screen can be dragged upwards with a mouse or touchscreen to unlock the device. Screen locking functionality is also built into screensaver systems on some Unix-like operating systems, such as XScreenSaver and gnome-screensaver.
Apple holds several patents related to the sliding lock screen used by its iOS devices: it was granted U.S. Patent 7,657,849 in 2010, and U.S. Patent 8,046,721 in 2011, describing a system that involves continuously dragging an image to a certain point to unlock the device. As part of ongoing patent wars between numerous companies surrounding patents related to mobile devices, Apple has asserted these patents in several patent infringement lawsuits outside the United States with competing vendors. However, its lawsuits with Samsung in the Netherlands and HTC in the United Kingdom both led to failure: both courts ruled the patents to be invalid, citing the similar lock screen on the N1, a mobile phone manufactured by the Swedish company Neonode, as prior art for Apple's design. The British court specifically ruled that Apple's lock screen was an "obvious improvement" over that of the Neonode N1 due to its additional visual feedback through an on-screen slider graphic (unlike the N1, which only displayed a written instruction explaining the gesture).
In January 2012, Apple won a permanent injunction from a German court after it ruled that Motorola Mobility violated the patents on some of its recent devices (although the Motorola Xoom tablet, was ruled to not have infringed on the patent). However, Apple was warned that they would have been required to put up a bond as insurance if they were to allow the injunction to take effect, and any potential sales ban as a result would be limited to Germany.
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