diff --git a/switchbot/devices/device.py b/switchbot/devices/device.py
index a80fb41..1970ef9 100644
--- a/switchbot/devices/device.py
+++ b/switchbot/devices/device.py
@@ -955,6 +955,12 @@ def _decrypt(self, data: bytearray) -> bytes:
         if len(data) == 0:
             return b""
         if self._iv is None:
+            if self._expected_disconnect:
+                _LOGGER.debug(
+                    "%s: Cannot decrypt, IV is None during expected disconnect",
+                    self.name,
+                )
+                return b""
             raise RuntimeError("Cannot decrypt: IV is None")
         decryptor = self._get_cipher().decryptor()
         return decryptor.update(data) + decryptor.finalize()
diff --git a/switchbot/devices/lock.py b/switchbot/devices/lock.py
index c8be891..1ac41f8 100644
--- a/switchbot/devices/lock.py
+++ b/switchbot/devices/lock.py
@@ -214,6 +214,12 @@ async def _disable_notifications(self) -> bool:
 
     def _notification_handler(self, _sender: int, data: bytearray) -> None:
         if self._notifications_enabled and self._check_command_result(data, 0, {0xF}):
+            if self._expected_disconnect:
+                _LOGGER.debug(
+                    "%s: Ignoring lock notification during expected disconnect",
+                    self.name,
+                )
+                return
             self._update_lock_status(data)
         else:
             super()._notification_handler(_sender, data)
diff --git a/tests/test_encrypted_device.py b/tests/test_encrypted_device.py
index 3ebfc88..1ed071a 100644
--- a/tests/test_encrypted_device.py
+++ b/tests/test_encrypted_device.py
@@ -365,3 +365,22 @@ async def test_empty_data_encryption_decryption() -> None:
     # Test empty decryption
     decrypted = device._decrypt(bytearray())
     assert decrypted == b""
+
+
+@pytest.mark.asyncio
+async def test_decrypt_with_none_iv_during_disconnect() -> None:
+    """Test that decryption returns empty bytes when IV is None during expected disconnect."""
+    device = create_encrypted_device()
+
+    # Simulate disconnection in progress
+    device._expected_disconnect = True
+    device._iv = None
+
+    # Should return empty bytes instead of raising
+    result = device._decrypt(bytearray(b"encrypted_data"))
+    assert result == b""
+
+    # Verify it still raises when not disconnecting
+    device._expected_disconnect = False
+    with pytest.raises(RuntimeError, match="Cannot decrypt: IV is None"):
+        device._decrypt(bytearray(b"encrypted_data"))
diff --git a/tests/test_lock.py b/tests/test_lock.py
index fc4f833..6994e95 100644
--- a/tests/test_lock.py
+++ b/tests/test_lock.py
@@ -1,3 +1,4 @@
+import logging
 from unittest.mock import AsyncMock, Mock, patch
 
 import pytest
@@ -478,6 +479,34 @@ def test_notification_handler_not_enabled(model: str):
         mock_super.assert_called_once()
 
 
+@pytest.mark.parametrize(
+    "model",
+    [
+        SwitchbotModel.LOCK,
+        SwitchbotModel.LOCK_LITE,
+        SwitchbotModel.LOCK_PRO,
+        SwitchbotModel.LOCK_ULTRA,
+    ],
+)
+def test_notification_handler_during_disconnect(
+    model: str, caplog: pytest.LogCaptureFixture
+) -> None:
+    """Test _notification_handler during expected disconnect."""
+    device = create_device_for_command_testing(model)
+    device._notifications_enabled = True
+    device._expected_disconnect = True
+    data = bytearray(b"\x0f\x00\x00\x00\x80\x00\x00\x00\x00\x00")
+    with (
+        patch.object(device, "_update_lock_status") as mock_update,
+        caplog.at_level(logging.DEBUG),
+    ):
+        device._notification_handler(0, data)
+        # Should not update lock status during disconnect
+        mock_update.assert_not_called()
+        # Should log debug message
+        assert "Ignoring lock notification during expected disconnect" in caplog.text
+
+
 @pytest.mark.parametrize(
     "model",
     [