Problem

Mobile devices must enter a lock/sleep state to reduce power consumption, prevent accidental input, and sometimes to prevent unauthorized input. The device must communicate this clearly, and assist with un-locking.

Solution

When locked or sleeping a Lock Screen or "Sleep Screen" will be displayed, with key information such as events, alerts, time and date, and instructions on how to unlock the device.

Lock screens are useful to prevent input, and power consumption is a real issue, but many lock screens go overboard. Backlight should be minimized or removed, but display drivers left on so retroreflective (ambient light) display is still possible. Pixel-illuminated technologies provide other possibilities.

Variations

The Lock Screen is displayed immediately after a deliberate (user initiated) lock, or when waking from sleep but not yet unlocked. A similar screen is the Sleep Screen, which often has no display at all. These can, and should, still display some information.

Certain newer technologies, such as OLED, have no backlight. Clever design can illuminate just a few pixels, at low power, and display all relevant Lock Screen information at a very low power level, combining it with a Sleep Screen.

Screens displayed when the device is off but charging, and similar special types of screens, are similar enough to Lock Screens to be considered the same pattern. Display any useful information available to the device. For example, if date and time are stored at a low enough level to be accessed at this point (and they usually are) then display that information, as well as the battery status message.

Interaction Details

Locking may occur based on an activity timer, or by deliberate user activation. Both systems are usually enabled. Deliberate user locking should use a hardware Lock key, which may be a short tap of the Power key. Menu selections and key combinations are usually so cumbersome as to be unused so should be avoided.

Some convertible devices (flip or slide form factor) only operate when open. These form factors will immediately lock when closed.

Unlocking may be accomplished via key input, screen interaction or . Most devices will require exiting the Sleep Screen first, and may only unlock once the unlock method is displayed on the Lock Screen. Many devices can use any of several methods, such as key input or sliding the keyboard open.

Unlock key input is usually a key combination (2 must be held down at once for a short time) or key pattern (2-4 keys must be pressed in sequence). These are not codes, but Sign On methods may also be used.

On screen unlocking for touch and pen devices uses a simple gesture, such as a drag action, which cannot be easily reproduced by accident.

Locking does not imply exiting or suspending applications. Even activities such as voice calls may continue when the Lock or Sleep Screens have activated. Careful consideration must be made to allow the user to unlock without interrupting the process, and to displaying relevant information about the ongoing activity.

Certain actions may also be allowed to take place without exiting the Lock Screen. An ongoing voice call may be terminated, for example. SMS messages received may be answered from the Lock Screen. These must be designed so they are unlikely to be activated by accident either by context (no ongoing call should be loose in the pocket, so End cannot be pressed by accident) or by requiring unlock-like action precision to initiate (responding to an SMS required tapping a small "respond" area, within a short time, and all other actions are disregarded).

Presentation Details

The Lock Screen will display the time of day, the complete Annunciator Row and any information or gesture targets to instruct or assist the user in unlocking. It should also indicate, iconically (a lock icon), in text ("Phone is locked"), or by the lack of conventional controls like Softkey tabs, that it is a Lock Screen. By default, display the backdrop from the [Home & Idle Screens, but users may customize this to be a different image.

The Sleep Screen should display much the same information, but especially the time. Unlock methods will be suppressed, unless the device can be unlocked directly from the Sleep Screen. Assure the display can be seen and used most efficiently by the display technology available. If relying on retroreflectivity, make sure the items are of maximum contrast. For OLED screens, use outlines and reduce the maximum pixel brightness. For ePaper, do not display the time unless partial screen refresh can be convincingly accomplished, without undue power drain.

Additional information about alerts or notifications may also be presented. The conventional Notifications methods should be used, except as they might interfere with the operation of the Lock Screen, or could not be viewed without access which would be difficult without unlocking the device. For example, a large Pop-Up dialogue on a touch screen might cover the unlock gesture area; a smaller item, or one may need to be developed for the Lock Screen.

Certain system messages may demand special screens. When the battery is dead, for example, the screen displayed should still follow the Lock and Sleep Screen concept. If the clock is available (it often is) display the time and date. Display the Annunicator Row even though everything will be disabled. Replace the unlock instructions with critical battery or charge state information instead.

If there is an external output for use with TVs or projectors, don't just send the same signal, but something more suitable to the large display. Avoid displaying details of notifications by default (to preserve privacy), do not display the Annunciator Row as that is about the device, not the display, and move the display elements around to prevent burn in.

Antipatterns

Mobiles are 24/7, always-on devices for their users. Do not dim the screen and/or cut display by default. Consider the actual power drain, and how else the true needs can be achieved.

Examples