Turn on screen on device

adb shell input keyevent KEYCODE_POWER

Works to turn on screen (when display is off) Works to turn off screen (when display is on/awake)

For Android 5.0 and above:

adb shell input keyevent KEYCODE_WAKEUP

or

adb shell input keyevent 224

KEYCODE_WAKEUP

Key code constant: Wakeup key. Wakes up the device. Behaves somewhat like KEYCODE_POWER but it has no effect if the device is already awake.

https://developer.android.com/reference/android/view/KeyEvent#KEYCODE_WAKEUP

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^{Note: KEYCODE_POWER has been added in API level 1, while KEYCODE_WAKEUP has been added in API level 20!}