Always on Display
Always On Display (AOD) is a smartphone feature that has the device continue to show limited information while the phone is asleep. It is widely available on Android handsets. On some Android phones, the feature is called Ambient Display or Active Display depending on its implementation and behavior. Depending on the phone's design, it may be a replacement feature or complementary to the Notification LED. Overview. A phone with AOD enabled keeps a limited portion of the screen on during sleep mode. Instead of the notification LED blinking to serve as an indicator for any incoming  messages or notifications which the user may need to check out, an Always On Display shows the time, date, and battery status by default, but can be configured to also show various types of notifications as they arrive or screensavers. Different Android brands and models have differing behavior for this feature. Some phones would have the screen off until new notifications arrive whereupon the display would either be active for a few seconds or remain on until the user interacts with the device to read or dismiss the notification (essentially having the entire screen serve as a larger notification LED ); others instead have the phone screen activate when it detects input, such as being picked up or the screen interacted with. These versions are usually called Ambient display, in contrast to a true Always On Display where at least part of the screen remains on at all times. Again depending on the manufacturer, not all apps may be supported for showing notifications with this feature - only first party apps or popular apps may be supported. History. This technology was first introduced by Nokia in on the 6303, and more widely adopted with its next generation AMOLED Symbian phones in 2010  (the Nokia N8, C7, C6-01 and E7). It became a standard feature on most Nokia Lumia Windows Phones in 2013, paired with the Nokia Glance Screen app. The feature has since become more widely available on Android handsets including Huawei (Mate 10 Pro, P20 Pro), Motorola (Moto X, Z, G), LG (G5, G6, G7, V30, V35, V40, V60), Samsung (Galaxy A3 (2017), A7 (2017, 2018), A30, A50, S7, S8, S9, S10, S20, S20 FE, S21, Note FE/8/9/10/20), and Google Pixel (Pixel 2, Pixel 3, Pixel 3a, Pixel 4, Pixel 4a, Pixel 5, Pixel 6 / 6 pro). Battery impact. The  Always On Display feature does consume energy, although the Samsung Galaxy S7 series phones, and later phones that made the feature popular are built with AMOLED screens that turn off black pixels. On today's AMOLED phone displays, it is true that only a few pixels may need to be turned on but they do need to be moved to prevent pixel burn in. Colors, sensors and processors all consume energy while AOD is in use, which leads to an extra consumption of roughly 3% battery. On LCD displays, the backlight has to be turned on, even if only a  part of the screen is showing information, so this feature consumes a significant amount of power compared to a notification LED. Typically, an ambient display solution which turns on the screen only when notifications are present, remains on, but turns off when they are dismissed will consume the least amount of battery power while still drawing the user's attention when required, in contrast to an Always-on Display which will keep the screen on, all of the time, to show some information, even if notifications may not be present. Since the date and time are less essential than battery  status or notifications which may require the user's immediate attention, an AOD can be customized in many app-based implementations to only show notifications or selectively choose what is shown. Scheduled on/off times. In some phones, the Always On Display/Ambient Display feature can be toggled on a schedule, such as during nighttime, or when the proximity sensor detects that the device is in a pocket. There may be an option for the phone to keep the screen on only when there are notifications to be acknowledged or dismissed by the user.