diff --git a/packages/SystemUI/aconfig/systemui.aconfig b/packages/SystemUI/aconfig/systemui.aconfig
index 41d12dc..b1b7902 100644
--- a/packages/SystemUI/aconfig/systemui.aconfig
+++ b/packages/SystemUI/aconfig/systemui.aconfig
@@ -145,6 +145,16 @@
 }
 
 flag {
+    name: "enable_background_keyguard_ondrawn_callback"
+    namespace: "systemui"
+    description: "Calls the onDrawn keyguard in the background, without being blocked by main"
+        "thread work. This results in the screen to turn on earlier when the main thread is stuck. "
+        "Note that, even after this callback is called, we're waiting for all windows to finish "
+        " drawing."
+    bug: "295873557"
+}
+
+flag {
     name: "qs_new_pipeline"
     namespace: "systemui"
     description: "Use the new pipeline for Quick Settings. Should have no behavior changes."
diff --git a/packages/SystemUI/src/com/android/keyguard/mediator/ScreenOnCoordinator.kt b/packages/SystemUI/src/com/android/keyguard/mediator/ScreenOnCoordinator.kt
index 603471b..7a560e8 100644
--- a/packages/SystemUI/src/com/android/keyguard/mediator/ScreenOnCoordinator.kt
+++ b/packages/SystemUI/src/com/android/keyguard/mediator/ScreenOnCoordinator.kt
@@ -19,6 +19,7 @@
 import android.annotation.BinderThread
 import android.os.Handler
 import android.os.Trace
+import com.android.systemui.Flags
 import com.android.systemui.dagger.SysUISingleton
 import com.android.systemui.dagger.qualifiers.Main
 import com.android.systemui.unfold.SysUIUnfoldComponent
@@ -59,8 +60,11 @@
         foldAodAnimationController?.onScreenTurningOn(pendingTasks.registerTask("fold-to-aod"))
 
         pendingTasks.onTasksComplete {
-            mainHandler.post {
+            if (Flags.enableBackgroundKeyguardOndrawnCallback()) {
+                // called by whatever thread completes the last task registered.
                 onDrawn.run()
+            } else {
+                mainHandler.post { onDrawn.run() }
             }
         }
         Trace.endSection()
diff --git a/packages/SystemUI/tests/src/com/android/keyguard/mediator/ScreenOnCoordinatorTest.kt b/packages/SystemUI/tests/src/com/android/keyguard/mediator/ScreenOnCoordinatorTest.kt
index 9fe32f1..b45c894 100644
--- a/packages/SystemUI/tests/src/com/android/keyguard/mediator/ScreenOnCoordinatorTest.kt
+++ b/packages/SystemUI/tests/src/com/android/keyguard/mediator/ScreenOnCoordinatorTest.kt
@@ -16,16 +16,21 @@
 
 package com.android.keyguard.mediator
 
-import android.os.Handler
 import android.os.Looper
+import android.platform.test.flag.junit.SetFlagsRule
+import android.platform.test.flag.junit.SetFlagsRule.DefaultInitValueType.DEVICE_DEFAULT
 import android.testing.AndroidTestingRunner
 import androidx.test.filters.SmallTest
+import com.android.systemui.Flags
 import com.android.systemui.SysuiTestCase
 import com.android.systemui.unfold.FoldAodAnimationController
 import com.android.systemui.unfold.SysUIUnfoldComponent
 import com.android.systemui.unfold.UnfoldLightRevealOverlayAnimation
 import com.android.systemui.util.mockito.capture
+import com.android.systemui.utils.os.FakeHandler
+import com.android.systemui.utils.os.FakeHandler.Mode.QUEUEING
 import org.junit.Before
+import org.junit.Rule
 import org.junit.Test
 import org.junit.runner.RunWith
 import org.mockito.ArgumentCaptor
@@ -52,10 +57,13 @@
     @Captor
     private lateinit var readyCaptor: ArgumentCaptor<Runnable>
 
-    private val testHandler = Handler(Looper.getMainLooper())
+    private val testHandler = FakeHandler(Looper.getMainLooper()).apply { setMode(QUEUEING) }
 
     private lateinit var screenOnCoordinator: ScreenOnCoordinator
 
+    @get:Rule
+    val setFlagsRule = SetFlagsRule(DEVICE_DEFAULT)
+
     @Before
     fun setUp() {
         MockitoAnnotations.initMocks(this)
@@ -77,7 +85,7 @@
 
         onUnfoldOverlayReady()
         onFoldAodReady()
-        waitHandlerIdle(testHandler)
+        waitHandlerIdle()
 
         // Should be called when both unfold overlay and keyguard drawn ready
         verify(runnable).run()
@@ -90,7 +98,7 @@
 
         onUnfoldOverlayReady()
         onFoldAodReady()
-        waitHandlerIdle(testHandler)
+        waitHandlerIdle()
 
         // Should be called when both unfold overlay and keyguard drawn ready
         verify(runnable).run()
@@ -104,7 +112,8 @@
 
         onUnfoldOverlayReady()
         onFoldAodReady()
-        waitHandlerIdle(testHandler)
+        waitHandlerIdle()
+
 
         // Should not be called because this screen turning on call is not valid anymore
         verify(runnable, never()).run()
@@ -112,13 +121,43 @@
 
     @Test
     fun testUnfoldTransitionDisabledDrawnTasksReady_onScreenTurningOn_callsDrawnCallback() {
+        setFlagsRule.disableFlags(Flags.FLAG_ENABLE_BACKGROUND_KEYGUARD_ONDRAWN_CALLBACK)
         // Recreate with empty unfoldComponent
         screenOnCoordinator = ScreenOnCoordinator(
             Optional.empty(),
             testHandler
         )
         screenOnCoordinator.onScreenTurningOn(runnable)
-        waitHandlerIdle(testHandler)
+        waitHandlerIdle()
+
+        // Should be called when only keyguard drawn
+        verify(runnable).run()
+    }
+    @Test
+    fun testUnfoldTransitionDisabledDrawnTasksReady_onScreenTurningOn_usesMainHandler() {
+        setFlagsRule.disableFlags(Flags.FLAG_ENABLE_BACKGROUND_KEYGUARD_ONDRAWN_CALLBACK)
+        // Recreate with empty unfoldComponent
+        screenOnCoordinator = ScreenOnCoordinator(
+                Optional.empty(),
+                testHandler
+        )
+        screenOnCoordinator.onScreenTurningOn(runnable)
+
+        // Never called as the main handler didn't schedule it yet.
+        verify(runnable, never()).run()
+    }
+
+    @Test
+    fun unfoldTransitionDisabledDrawnTasksReady_onScreenTurningOn_bgCallback_callsDrawnCallback() {
+        setFlagsRule.enableFlags(Flags.FLAG_ENABLE_BACKGROUND_KEYGUARD_ONDRAWN_CALLBACK)
+        // Recreate with empty unfoldComponent
+        screenOnCoordinator = ScreenOnCoordinator(
+                Optional.empty(),
+                testHandler
+        )
+        screenOnCoordinator.onScreenTurningOn(runnable)
+        // No need to wait for the handler to be idle, as it shouldn't be used
+        // waitHandlerIdle()
 
         // Should be called when only keyguard drawn
         verify(runnable).run()
@@ -134,7 +173,7 @@
         readyCaptor.value.run()
     }
 
-    private fun waitHandlerIdle(handler: Handler) {
-        handler.runWithScissors({},  /* timeout= */ 0)
+    private fun waitHandlerIdle() {
+        testHandler.dispatchQueuedMessages()
     }
 }