diff --git a/changelogs/fragments/1440-cloudwatch_metric_alarm-fix-change-detection.yml b/changelogs/fragments/1440-cloudwatch_metric_alarm-fix-change-detection.yml
new file mode 100644
index 00000000000..0cbde555d32
--- /dev/null
+++ b/changelogs/fragments/1440-cloudwatch_metric_alarm-fix-change-detection.yml
@@ -0,0 +1,2 @@
+bugfixes:
+- cloudwatch_metric_alarm - Don't consider ``StateTransitionedTimestamp`` in change detection. (https://github.com/ansible-collections/amazon.aws/pull/1440).
diff --git a/plugins/modules/cloudwatch_metric_alarm.py b/plugins/modules/cloudwatch_metric_alarm.py
index 714330ce43e..418d5ea93c0 100644
--- a/plugins/modules/cloudwatch_metric_alarm.py
+++ b/plugins/modules/cloudwatch_metric_alarm.py
@@ -333,8 +333,10 @@ def create_metric_alarm(connection, module, params):
         if 'TreatMissingData' not in alarm.keys():
             alarm['TreatMissingData'] = 'missing'
 
+        # Exclude certain props from change detection
         for key in ['ActionsEnabled', 'StateValue', 'StateReason',
                     'StateReasonData', 'StateUpdatedTimestamp',
+                    'StateTransitionedTimestamp',
                     'AlarmArn', 'AlarmConfigurationUpdatedTimestamp', 'Metrics']:
             alarm.pop(key, None)
         if alarm != params: