diff --git a/mobly/asserts.py b/mobly/asserts.py
index e877e05f..014847bf 100644
--- a/mobly/asserts.py
+++ b/mobly/asserts.py
@@ -15,6 +15,7 @@
 import re
 import unittest
 
+from mobly import logger
 from mobly import signals
 
 # Have an instance of unittest.TestCase so we could reuse some logic
@@ -23,6 +24,21 @@
 _pyunit_proxy.maxDiff = None
 
 
+def _add_key_frame(extras, action, details):
+  """Helper to inject key frame data into assertion extras."""
+  key_frame_data = {
+      'event_type': 'key_frame',
+      'action': action,
+      'timestamp': logger.get_log_line_timestamp(),
+      'details': details,
+  }
+  if extras is None:
+    extras = {}
+  if isinstance(extras, dict):
+    extras['key_frame'] = key_frame_data
+  return extras
+
+
 def _call_unittest_assertion(
     assertion_method, *args, msg=None, extras=None, **kwargs
 ):
@@ -47,6 +63,7 @@ def _call_unittest_assertion(
   # This raise statement is outside of the above except statement to
   # prevent Python3's exception message from having two tracebacks.
   if my_msg is not None:
+    extras = _add_key_frame(extras, assertion_method.__name__, msg)
     raise signals.TestFailure(my_msg, extras=extras)
 
 
@@ -438,6 +455,7 @@ def fail(msg, extras=None):
   Raises:
     signals.TestFailure: Mark a test as failed.
   """
+  extras = _add_key_frame(extras, 'fail', msg)
   raise signals.TestFailure(msg, extras)
 
 
diff --git a/tests/mobly/base_test_test.py b/tests/mobly/base_test_test.py
index f3891335..070f9568 100755
--- a/tests/mobly/base_test_test.py
+++ b/tests/mobly/base_test_test.py
@@ -585,7 +585,7 @@ def test_something(self):
     self.assertEqual(actual_record.test_name, self.mock_test_name)
     self.assertEqual(actual_record.details, MSG_EXPECTED_EXCEPTION)
     self.assertTrue(actual_record.end_time)
-    self.assertIsNone(actual_record.extras)
+    self.assertIn('key_frame', actual_record.extras)
     expected_summary = (
         'Error 1, Executed 1, Failed 0, Passed 0, Requested 1, Skipped 0'
     )
@@ -626,7 +626,7 @@ def test_something(self):
     actual_record = bt_cls.results.error[0]
     self.assertEqual(actual_record.test_name, self.mock_test_name)
     self.assertEqual(actual_record.details, MSG_EXPECTED_EXCEPTION)
-    self.assertIsNone(actual_record.extras)
+    self.assertIn('key_frame', actual_record.extras)
     self.assertFalse(actual_record.extra_errors)
     self.assertTrue(actual_record.end_time)
     expected_summary = (
@@ -761,7 +761,7 @@ def test_something(self):
     actual_record = bt_cls.results.failed[0]
     self.assertEqual(actual_record.test_name, self.mock_test_name)
     self.assertEqual(actual_record.details, MSG_EXPECTED_EXCEPTION)
-    self.assertIsNone(actual_record.extras)
+    self.assertIn('key_frame', actual_record.extras)
     expected_summary = (
         'Error 0, Executed 1, Failed 1, Passed 0, Requested 1, Skipped 0'
     )
@@ -935,7 +935,7 @@ def test_something(self):
     self.assertIn('on_fail', actual_record.extra_errors)
     self.assertEqual(actual_record.test_name, self.mock_test_name)
     self.assertEqual(actual_record.details, MSG_EXPECTED_EXCEPTION)
-    self.assertIsNone(actual_record.extras)
+    self.assertIn('key_frame', actual_record.extras)
     expected_summary = (
         'Error 0, Executed 1, Failed 1, Passed 0, Requested 1, Skipped 0'
     )
@@ -985,7 +985,7 @@ def test_something(self):
         actual_record.extra_errors['teardown_test'].details,
         MSG_EXPECTED_EXCEPTION,
     )
-    self.assertIsNone(actual_record.extra_errors['teardown_test'].extras)
+    self.assertIn('key_frame', actual_record.extra_errors['teardown_test'].extras)
     expected_summary = (
         'Error 1, Executed 1, Failed 0, Passed 0, Requested 1, Skipped 0'
     )
@@ -1059,7 +1059,7 @@ def test_something(self):
         actual_record.extra_errors['teardown_test'].details,
         MSG_EXPECTED_EXCEPTION,
     )
-    self.assertIsNone(actual_record.extra_errors['teardown_test'].extras)
+    self.assertIn('key_frame', actual_record.extra_errors['teardown_test'].extras)
     expected_summary = (
         'Error 1, Executed 1, Failed 0, Passed 0, Requested 1, Skipped 0'
     )
@@ -2006,7 +2006,7 @@ def test_func(self):
     actual_record = bt_cls.results.failed[0]
     self.assertEqual(actual_record.test_name, 'test_func')
     self.assertEqual(actual_record.details, 'failed from assert_true')
-    self.assertIsNone(actual_record.extras)
+    self.assertIn('key_frame', actual_record.extras)
 
   def test_unpack_userparams_required(self):
     """Missing a required param should raise an error."""