diff --git a/docs/examples/create_device_with_issued_sim.py b/docs/examples/create_device_with_issued_sim.py
new file mode 100644
index 0000000..df9633c
--- /dev/null
+++ b/docs/examples/create_device_with_issued_sim.py
@@ -0,0 +1,28 @@
+# * Import SDK package
+from emnify import EMnify
+
+#  Initiate instance
+
+emnify_client = EMnify("YOUR APP TOKEN")
+"""
+=== Create a disabled device with a SIM that stays in ISSUED status ===
+"""
+# When a sim object is provided the API activates the SIM by default, and an
+# activated SIM is billed even while the device is disabled. Pass
+# `activate: False` to assign the SIM without activating it.
+service_profile = emnify_client.devices.service_profile_model(id=1)
+tariff_profile = emnify_client.devices.tariff_profile_model(id=1)
+device_status = emnify_client.devices.status_model(id=1, description="Disabled")
+device_model = emnify_client.devices.device_create_model(
+    name="my-device",
+    tariff_profile=tariff_profile,
+    status=device_status,
+    service_profile=service_profile,
+    # pass a plain dict - the SimList model has no `activate` field and would drop it
+    sim={"id": 1, "activate": False},
+)
+
+device_id = emnify_client.devices.create_device(device_model)
+
+# The SIM is assigned to the device and still in ISSUED status
+print(emnify_client.sim.retrieve_sim(sim_id=1).status)
diff --git a/docs/examples/device_lifecycle_management.py b/docs/examples/device_lifecycle_management.py
index fa26967..4c94825 100644
--- a/docs/examples/device_lifecycle_management.py
+++ b/docs/examples/device_lifecycle_management.py
@@ -132,8 +132,10 @@
 
 device_to_delete = list(
     filter(
-        lambda device: device.sim
-        and device.status.id == emnify_constants.DeviceStatuses.ENABLED_ID,
+        lambda device: (
+            device.sim
+            and device.status.id == emnify_constants.DeviceStatuses.ENABLED_ID
+        ),
         old_devices_list,
     )
 )[0]
diff --git a/docs/examples/local_debug.py b/docs/examples/local_debug.py
index 55203c0..b606770 100644
--- a/docs/examples/local_debug.py
+++ b/docs/examples/local_debug.py
@@ -5,19 +5,21 @@
 import sys
 
 # Add the path to the module to the Python path, below it's set to Docker workdir
-sys.path.append('/sdk')
+sys.path.append("/sdk")
 # Import package
 from emnify import EMnify
 
 # Get the token from environment variable
-TOKEN = os.environ.get('EMNIFY_SDK_APPLICATION_TOKEN')
+TOKEN = os.environ.get("EMNIFY_SDK_APPLICATION_TOKEN")
 
 # Initiate SDK instance using application token
 emnify = EMnify(TOKEN)
 
+
 def get_iterator_length(iterator):
     return len(list(iterator))
 
+
 # Execute a command against desired API
 devices = emnify.devices.get_devices_list()
 #
diff --git a/emnify/modules/device/models.py b/emnify/modules/device/models.py
index 8f83faa..767ac5e 100644
--- a/emnify/modules/device/models.py
+++ b/emnify/modules/device/models.py
@@ -10,6 +10,7 @@
 class SimDevice(BaseModel):
     id: int
     status: Optional[generated_models.Status] = None
+    activate: Optional[bool] = None
 
 
 class Device(generated_models.Endpoint):
diff --git a/pyproject.toml b/pyproject.toml
index b0f0765..9aecf1d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,3 +1,9 @@
 [build-system]
 requires = ["setuptools>=42"]
 build-backend = "setuptools.build_meta"
+
+[tool.ruff]
+extend-exclude = ["emnify/version.py"]
+
+[tool.ruff.lint]
+select = ["E4", "E7", "E9", "F"]
diff --git a/tests/test_emnify.py b/tests/test_emnify.py
index fd489f8..328b6a3 100644
--- a/tests/test_emnify.py
+++ b/tests/test_emnify.py
@@ -170,6 +170,32 @@ def test_create_device_with_sim(self):
         response = emnify.devices.create_device(device=device)
         self.assertEqual(response, 11380016)
 
+    def test_create_device_sim_activate_is_serialized(self):
+        """`sim.activate` must reach the request body so callers can assign a
+        SIM without activating it."""
+        emnify = emnify_client(app_token=self.token)
+
+        def build_sim_payload(sim):
+            device = emnify.devices.device_create_model(
+                name="test-device",
+                status=emnify.devices.status_model(id=1, description="Disabled"),
+                service_profile=emnify.devices.service_profile_model(id=1),
+                tariff_profile=emnify.devices.tariff_profile_model(id=2),
+                sim=sim,
+            )
+            return device.dict(exclude_none=True)["sim"]
+
+        self.assertEqual(
+            build_sim_payload({"id": 250, "activate": False}),
+            {"id": 250, "activate": False},
+        )
+        self.assertEqual(
+            build_sim_payload({"id": 250, "activate": True}),
+            {"id": 250, "activate": True},
+        )
+        # omitted -> not sent, so the API default applies
+        self.assertEqual(build_sim_payload({"id": 250}), {"id": 250})
+
     @vcr_instance.use_cassette(
         "tests/fixtures/cassettes/test_activate_disactivate_device.yaml"
     )