diff --git a/stock_lot_serial_no_default/README.rst b/stock_lot_serial_no_default/README.rst
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+===========================
+Stock Lot/Serial No Default
+===========================
+
+This module modifies Odoo's default behavior for products tracked by serial numbers.
+
+Problem
+=======
+
+In standard Odoo, when products are tracked by serial numbers, the system automatically:
+
+* Picks an available serial number when reserving stock (clicking "Check Availability")
+* Pre-fills this serial number in delivery orders, stock transfers, and manufacturing orders
+* Proposes the serial number to staff without requiring conscious selection
+
+This can lead to situations where staff processes transfers without verifying they have the correct physical item.
+
+Solution
+========
+
+This module prevents automatic serial number selection while maintaining quantity reservation:
+
+* **Quantities are still reserved** - inventory levels are correctly tracked
+* **Serial numbers are NOT pre-filled** - fields remain empty after reservation
+* **Staff must manually enter serial numbers** - ensures conscious selection of physical items
+* **No validation added** - staff can still complete operations (following your workflow requirements)
+
+Technical Details
+=================
+
+The module overrides the ``_update_reserved_quantity_vals`` method in ``stock.move`` model:
+
+* For products with ``tracking='serial'``, the ``lot_id`` parameter is cleared
+* Move lines are created without pre-assigned serial numbers
+* Works for all stock operations: deliveries, transfers, and manufacturing orders
+
+Configuration
+=============
+
+No configuration needed. The module works automatically for all products tracked by serial number.
+
+Usage
+=====
+
+1. You may need to enable Settings -> inventory -> Lots & Serial Numbers
+2. Create a product and set Track Inventory By Unique Serial Number
+3. Create a delivery order / stock transfer / manufacturing order for serial-tracked products
+4. Click "Check Availability" to reserve stock
+5. The quantity will be reserved but serial number fields will be empty. In delivery orders you might need to enable the column "Serial Number" if it's not shown by default.
+6. Staff must manually scan or enter the serial number for each item
+7. Validate the operation as usual
diff --git a/stock_lot_serial_no_default/__init__.py b/stock_lot_serial_no_default/__init__.py
new file mode 100644
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+++ b/stock_lot_serial_no_default/__init__.py
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+from . import models
diff --git a/stock_lot_serial_no_default/__manifest__.py b/stock_lot_serial_no_default/__manifest__.py
new file mode 100644
index 00000000..603d57e4
--- /dev/null
+++ b/stock_lot_serial_no_default/__manifest__.py
@@ -0,0 +1,16 @@
+{
+    "name": "Stock Lot/Serial No Default",
+    "version": "18.0.1.0.0",
+    "category": "Inventory/Inventory",
+    "summary": "Prevent automatic serial number selection in stock operations",
+    "author": "Nitrokey GmbH",
+    "website": "https://www.github.com/nitrokey/odoo-modules/",
+    "license": "AGPL-3",
+    "depends": [
+        "stock",
+    ],
+    "data": [],
+    "installable": True,
+    "application": False,
+    "auto_install": False,
+}
diff --git a/stock_lot_serial_no_default/models/__init__.py b/stock_lot_serial_no_default/models/__init__.py
new file mode 100644
index 00000000..6bda2d24
--- /dev/null
+++ b/stock_lot_serial_no_default/models/__init__.py
@@ -0,0 +1 @@
+from . import stock_move
diff --git a/stock_lot_serial_no_default/models/stock_move.py b/stock_lot_serial_no_default/models/stock_move.py
new file mode 100644
index 00000000..935bc7c9
--- /dev/null
+++ b/stock_lot_serial_no_default/models/stock_move.py
@@ -0,0 +1,38 @@
+from odoo import models
+
+
+class StockMove(models.Model):
+    _inherit = "stock.move"
+
+    def _update_reserved_quantity_vals(
+        self,
+        need,
+        location_id,
+        lot_id=None,
+        package_id=None,
+        owner_id=None,
+        strict=True,
+    ):
+        """Override to prevent automatic serial number assignment.
+
+        For products tracked by serial number, we still reserve the quantity
+        but do NOT assign a specific lot_id. This forces staff to manually
+        enter the serial number when processing the operation.
+        """
+        # Get the move line vals from parent
+        move_line_vals, taken_quantity = super()._update_reserved_quantity_vals(
+            need,
+            location_id,
+            lot_id=lot_id,
+            package_id=package_id,
+            owner_id=owner_id,
+            strict=strict,
+        )
+
+        # For serial-tracked products, clear the lot_id from the move line vals
+        if self.product_id.tracking == "serial":
+            for vals in move_line_vals:
+                vals["lot_id"] = False
+                vals["lot_name"] = False
+
+        return move_line_vals, taken_quantity
diff --git a/stock_lot_serial_no_default/tests/__init__.py b/stock_lot_serial_no_default/tests/__init__.py
new file mode 100644
index 00000000..3bff88bd
--- /dev/null
+++ b/stock_lot_serial_no_default/tests/__init__.py
@@ -0,0 +1 @@
+from . import test_serial_control
diff --git a/stock_lot_serial_no_default/tests/test_serial_control.py b/stock_lot_serial_no_default/tests/test_serial_control.py
new file mode 100644
index 00000000..65c95e73
--- /dev/null
+++ b/stock_lot_serial_no_default/tests/test_serial_control.py
@@ -0,0 +1,280 @@
+from odoo.tests import TransactionCase, tagged
+
+
+@tagged("post_install", "-at_install")
+class TestStockLotSerialNoDefault(TransactionCase):
+    """Test that serial numbers are not automatically assigned during reservation."""
+
+    @classmethod
+    def setUpClass(cls):
+        super().setUpClass()
+
+        # Create locations
+        cls.stock_location = cls.env.ref("stock.stock_location_stock")
+        cls.customer_location = cls.env.ref("stock.stock_location_customers")
+
+        # Create a product tracked by serial number
+        cls.product_serial = cls.env["product.product"].create(
+            {
+                "name": "Test Product Serial",
+                "type": "consu",
+                "is_storable": True,
+                "tracking": "serial",
+                "categ_id": cls.env.ref("product.product_category_all").id,
+            }
+        )
+
+        # Create a product tracked by lot
+        cls.product_lot = cls.env["product.product"].create(
+            {
+                "name": "Test Product Lot",
+                "type": "consu",
+                "is_storable": True,
+                "tracking": "lot",
+                "categ_id": cls.env.ref("product.product_category_all").id,
+            }
+        )
+
+        # Create a product without tracking
+        cls.product_none = cls.env["product.product"].create(
+            {
+                "name": "Test Product No Tracking",
+                "type": "consu",
+                "is_storable": True,
+                "tracking": "none",
+                "categ_id": cls.env.ref("product.product_category_all").id,
+            }
+        )
+
+        # Create serial numbers for the serial-tracked product
+        cls.serial_1 = cls.env["stock.lot"].create(
+            {
+                "name": "SERIAL-001",
+                "product_id": cls.product_serial.id,
+                "company_id": cls.env.company.id,
+            }
+        )
+        cls.serial_2 = cls.env["stock.lot"].create(
+            {
+                "name": "SERIAL-002",
+                "product_id": cls.product_serial.id,
+                "company_id": cls.env.company.id,
+            }
+        )
+
+        # Create lot for the lot-tracked product
+        cls.lot_1 = cls.env["stock.lot"].create(
+            {
+                "name": "LOT-001",
+                "product_id": cls.product_lot.id,
+                "company_id": cls.env.company.id,
+            }
+        )
+
+        # Add stock for all products
+        cls.env["stock.quant"]._update_available_quantity(
+            cls.product_serial,
+            cls.stock_location,
+            1.0,
+            lot_id=cls.serial_1,
+        )
+        cls.env["stock.quant"]._update_available_quantity(
+            cls.product_serial,
+            cls.stock_location,
+            1.0,
+            lot_id=cls.serial_2,
+        )
+        cls.env["stock.quant"]._update_available_quantity(
+            cls.product_lot,
+            cls.stock_location,
+            10.0,
+            lot_id=cls.lot_1,
+        )
+        cls.env["stock.quant"]._update_available_quantity(
+            cls.product_none,
+            cls.stock_location,
+            100.0,
+        )
+
+    def test_serial_no_automatic_assignment(self):
+        """Test that serial numbers are NOT automatically assigned."""
+        # Create a picking for serial-tracked product
+        picking = self.env["stock.picking"].create(
+            {
+                "location_id": self.stock_location.id,
+                "location_dest_id": self.customer_location.id,
+                "picking_type_id": self.env.ref("stock.picking_type_out").id,
+            }
+        )
+
+        # Create a move for 1 unit of serial-tracked product
+        move = self.env["stock.move"].create(
+            {
+                "name": "Test Move Serial",
+                "product_id": self.product_serial.id,
+                "product_uom_qty": 1.0,
+                "product_uom": self.product_serial.uom_id.id,
+                "picking_id": picking.id,
+                "location_id": self.stock_location.id,
+                "location_dest_id": self.customer_location.id,
+            }
+        )
+
+        # Confirm the picking
+        picking.action_confirm()
+
+        # Reserve stock (this is where automatic assignment would happen)
+        picking.action_assign()
+
+        # Verify the move is assigned (reserved)
+        self.assertEqual(
+            move.state,
+            "assigned",
+            "Move should be in assigned state after reservation",
+        )
+
+        # CRITICAL TEST: Verify that move lines exist but have NO lot_id
+        self.assertTrue(
+            move.move_line_ids,
+            "Move lines should be created after reservation",
+        )
+        for move_line in move.move_line_ids:
+            self.assertFalse(
+                move_line.lot_id,
+                "Serial number should NOT be automatically assigned to move line",
+            )
+            self.assertEqual(
+                move_line.quantity,
+                1.0,
+                "Reserved quantity should be 1.0 even without lot_id assignment",
+            )
+
+    def test_lot_tracking_still_works(self):
+        """Test that lot-tracked products still get automatic assignment."""
+        # Create a picking for lot-tracked product
+        picking = self.env["stock.picking"].create(
+            {
+                "location_id": self.stock_location.id,
+                "location_dest_id": self.customer_location.id,
+                "picking_type_id": self.env.ref("stock.picking_type_out").id,
+            }
+        )
+
+        # Create a move for lot-tracked product
+        move = self.env["stock.move"].create(
+            {
+                "name": "Test Move Lot",
+                "product_id": self.product_lot.id,
+                "product_uom_qty": 5.0,
+                "product_uom": self.product_lot.uom_id.id,
+                "picking_id": picking.id,
+                "location_id": self.stock_location.id,
+                "location_dest_id": self.customer_location.id,
+            }
+        )
+
+        # Confirm and reserve
+        picking.action_confirm()
+        picking.action_assign()
+
+        # Verify lot-tracked products still get automatic assignment
+        self.assertEqual(move.state, "assigned")
+        self.assertTrue(move.move_line_ids)
+        # For lot tracking, the lot_id should still be assigned
+        lot_assigned = any(ml.lot_id for ml in move.move_line_ids)
+        self.assertTrue(
+            lot_assigned,
+            "Lot-tracked products should still get automatic lot assignment",
+        )
+
+    def test_no_tracking_still_works(self):
+        """Test that products without tracking still work normally."""
+        # Create a picking for non-tracked product
+        picking = self.env["stock.picking"].create(
+            {
+                "location_id": self.stock_location.id,
+                "location_dest_id": self.customer_location.id,
+                "picking_type_id": self.env.ref("stock.picking_type_out").id,
+            }
+        )
+
+        # Create a move
+        move = self.env["stock.move"].create(
+            {
+                "name": "Test Move No Tracking",
+                "product_id": self.product_none.id,
+                "product_uom_qty": 10.0,
+                "product_uom": self.product_none.uom_id.id,
+                "picking_id": picking.id,
+                "location_id": self.stock_location.id,
+                "location_dest_id": self.customer_location.id,
+            }
+        )
+
+        # Confirm and reserve
+        picking.action_confirm()
+        picking.action_assign()
+
+        # Verify normal reservation works
+        self.assertEqual(move.state, "assigned")
+        self.assertTrue(move.move_line_ids)
+        self.assertEqual(
+            sum(move.move_line_ids.mapped("quantity")),
+            10.0,
+            "Full quantity should be reserved for non-tracked products",
+        )
+
+    def test_manual_serial_entry_still_possible(self):
+        """Test that staff can manually enter serial numbers after reservation."""
+        # Create and reserve a picking
+        picking = self.env["stock.picking"].create(
+            {
+                "location_id": self.stock_location.id,
+                "location_dest_id": self.customer_location.id,
+                "picking_type_id": self.env.ref("stock.picking_type_out").id,
+            }
+        )
+
+        move = self.env["stock.move"].create(
+            {
+                "name": "Test Move Serial Manual",
+                "product_id": self.product_serial.id,
+                "product_uom_qty": 1.0,
+                "product_uom": self.product_serial.uom_id.id,
+                "picking_id": picking.id,
+                "location_id": self.stock_location.id,
+                "location_dest_id": self.customer_location.id,
+            }
+        )
+
+        picking.action_confirm()
+        picking.action_assign()
+
+        # Manually assign a serial number to a move line
+        move_line = move.move_line_ids[0]
+        move_line.write(
+            {
+                "lot_id": self.serial_1.id,
+                "quantity": 1.0,
+            }
+        )
+
+        # Verify manual assignment works
+        self.assertEqual(
+            move_line.lot_id.id,
+            self.serial_1.id,
+            "Manual serial number assignment should work",
+        )
+        self.assertEqual(
+            move_line.quantity,
+            1.0,
+            "Manual quantity assignment should work",
+        )
+
+        # Verify picking can be validated with manual serial entry
+        picking.button_validate()
+        self.assertEqual(
+            picking.state,
+            "done",
+            "Picking should be completed after manual serial entry",
+        )