diff --git a/backend/tasks/models.py b/backend/tasks/models.py
index c848e00..97a2c4b 100644
--- a/backend/tasks/models.py
+++ b/backend/tasks/models.py
@@ -81,6 +81,11 @@ class Todo(Task):
     priority = models.PositiveSmallIntegerField(choices=EisenhowerMatrix.choices, default=EisenhowerMatrix.NOT_IMPORTANT_NOT_URGENT)
 
     def save(self, *args, **kwargs):
+        done_list_name = "Done"
+        if self.list_board.name == done_list_name:
+            self.completed = True
+            Todo.objects.filter(list_board=self.list_board).update(completed=True)
+
         if self.completed and not self.completion_date:
             self.completion_date = timezone.now()
         elif not self.completed:
diff --git a/backend/tasks/tests/test_todo_signal.py b/backend/tasks/tests/test_todo_signal.py
new file mode 100644
index 0000000..fa7fba5
--- /dev/null
+++ b/backend/tasks/tests/test_todo_signal.py
@@ -0,0 +1,33 @@
+from datetime import datetime, timedelta
+from django.urls import reverse
+from rest_framework import status
+from rest_framework.test import APITestCase
+from tasks.tests.utils import create_test_user
+from tasks.models import Todo
+from boards.models import ListBoard, Board
+
+
+class TodoSignalHandlersTests(APITestCase):
+    def setUp(self):
+        self.user = create_test_user()
+        self.client.force_authenticate(user=self.user)
+        self.list_board = Board.objects.get(user=self.user).listboard_set.first()
+
+    def test_update_priority_signal_handler(self):
+        """
+        Test the behavior of the update_priority signal handler.
+        """
+        due_date = datetime.now() + timedelta(days=5)
+        data = {
+            'title': 'Test Task',
+            'type': 'habit',
+            'difficulty': 1,
+            'end_event': due_date.strftime('%Y-%m-%dT%H:%M:%S'),
+            'list_board': self.list_board.id,
+        }
+        response = self.client.post(reverse("todo-list"), data, format='json')
+        self.assertEqual(response.status_code, status.HTTP_201_CREATED)
+
+        # Retrieve the created task and check if priority is updated
+        task = Todo.objects.get(title='Test Task')
+        self.assertIsNotNone(task.priority)  # Check if priority is not None
\ No newline at end of file