diff --git a/README.md b/README.md
@@ -228,7 +228,7 @@ The following devices have been tested and confirmed as working. If your device
 
 - **Plugs**: EP10, EP25<sup>\*</sup>, HS100<sup>\*\*</sup>, HS103, HS105, HS110, KP100, KP105, KP115, KP125, KP125M<sup>\*</sup>, KP401
 - **Power Strips**: EP40, HS107, HS300, KP200, KP303, KP400
-- **Wall Switches**: ES20M, HS200, HS210, HS220, KP405, KS200M, KS205<sup>\*</sup>, KS220M, KS225<sup>\*</sup>, KS230
+- **Wall Switches**: ES20M, HS200, HS210, HS220, KP405, KS200M, KS205<sup>\*</sup>, KS220M, KS225<sup>\*</sup>, KS230, KS240<sup>\*</sup>
 - **Bulbs**: KL110, KL120, KL125, KL130, KL135, KL50, KL60, LB110
 - **Light Strips**: KL400L5, KL420L5, KL430
 - **Hubs**: KH100<sup>\*</sup>

diff --git a/SUPPORTED.md b/SUPPORTED.md
@@ -88,6 +88,9 @@ Some newer Kasa devices require authentication. These are marked with <sup>*</su
   - Hardware: 1.0 (US) / Firmware: 1.0.2<sup>\*</sup>
 - **KS230**
   - Hardware: 1.0 (US) / Firmware: 1.0.14
+- **KS240**
+  - Hardware: 1.0 (US) / Firmware: 1.0.4<sup>\*</sup>
+  - Hardware: 1.0 (US) / Firmware: 1.0.5<sup>\*</sup>
 
 ### Bulbs
 

diff --git a/kasa/smart/modules/brightness.py b/kasa/smart/modules/brightness.py
@@ -57,3 +57,7 @@ async def set_brightness(self, brightness: int):
             )
 
         return await self.call("set_device_info", {"brightness": brightness})
+
+    async def _check_supported(self):
+        """Additional check to see if the module is supported by the device."""
+        return "brightness" in self.data
diff --git a/kasa/smart/modules/fanmodule.py b/kasa/smart/modules/fanmodule.py
@@ -68,3 +68,7 @@ def sleep_mode(self) -> bool:
     async def set_sleep_mode(self, on: bool):
         """Set sleep mode."""
         return await self.call("set_device_info", {"fan_sleep_mode_on": on})
+
+    async def _check_supported(self):
+        """Is the module available on this device."""
+        return "fan_speed_level" in self.data
diff --git a/kasa/smart/modules/lighttransitionmodule.py b/kasa/smart/modules/lighttransitionmodule.py
@@ -103,6 +103,8 @@ def turn_on_transition(self) -> int:
 
         Available only from v2.
         """
+        if "fade_on_time" in self._device.sys_info:
+            return self._device.sys_info["fade_on_time"]
         return self._turn_on["duration"]
 
     @property
@@ -138,6 +140,8 @@ def turn_off_transition(self) -> int:
 
         Available only from v2.
         """
+        if "fade_off_time" in self._device.sys_info:
+            return self._device.sys_info["fade_off_time"]
         return self._turn_off["duration"]
 
     @property
@@ -166,3 +170,11 @@ async def set_turn_off_transition(self, seconds: int):
             "set_on_off_gradually_info",
             {"off_state": {**self._turn_on, "duration": seconds}},
         )
+
+    def query(self) -> dict:
+        """Query to execute during the update cycle."""
+        # Some devices have the required info in the device info.
+        if "gradually_on_mode" in self._device.sys_info:
+            return {}
+        else:
+            return {self.QUERY_GETTER_NAME: None}
diff --git a/kasa/smart/smartdevice.py b/kasa/smart/smartdevice.py
@@ -22,6 +22,12 @@
 if TYPE_CHECKING:
     from .smartmodule import SmartModule
 
+# List of modules that wall switches with children, i.e. ks240 report on
+# the child but only work on the parent.  See longer note below in _initialize_modules.
+# This list should be updated when creating new modules that could have the
+# same issue, homekit perhaps?
+WALL_SWITCH_PARENT_ONLY_MODULES = [DeviceModule, TimeModule, Firmware, CloudModule]  # noqa: F405
+
 
 class SmartDevice(Device):
     """Base class to represent a SMART protocol based device."""
@@ -78,6 +84,9 @@ async def _initialize_children(self):
     @property
     def children(self) -> Sequence[SmartDevice]:
         """Return list of children."""
+        # Wall switches with children report all modules on the parent only
+        if self.device_type == DeviceType.WallSwitch:
+            return []
         return list(self._children.values())
 
     def _try_get_response(self, responses: dict, request: str, default=None) -> dict:
@@ -162,17 +171,32 @@ async def _initialize_modules(self):
         """Initialize modules based on component negotiation response."""
         from .smartmodule import SmartModule
 
+        # Some wall switches (like ks240) are internally presented as having child
+        # devices which report the child's components on the parent's sysinfo, even
+        # when they need to be accessed through the children.
+        # The logic below ensures that such devices report all but whitelisted, the
+        # child modules at the parent level to create an illusion of a single device.
+        if self._parent and self._parent.device_type == DeviceType.WallSwitch:
+            modules = self._parent.modules
+            skip_parent_only_modules = True
+        else:
+            modules = self.modules
+            skip_parent_only_modules = False
+
         for mod in SmartModule.REGISTERED_MODULES.values():
             _LOGGER.debug("%s requires %s", mod, mod.REQUIRED_COMPONENT)
+
+            if skip_parent_only_modules and mod in WALL_SWITCH_PARENT_ONLY_MODULES:
+                continue
             if mod.REQUIRED_COMPONENT in self._components:
                 _LOGGER.debug(
                     "Found required %s, adding %s to modules.",
                     mod.REQUIRED_COMPONENT,
                     mod.__name__,
                 )
                 module = mod(self, mod.REQUIRED_COMPONENT)
-                if await module._check_supported():
-                    self.modules[module.name] = module
+                if module.name not in modules and await module._check_supported():
+                    modules[module.name] = module
 
     async def _initialize_features(self):
         """Initialize device features."""
@@ -568,6 +592,8 @@ def _get_device_type_from_components(
             return DeviceType.Plug
         if "light_strip" in components:
             return DeviceType.LightStrip
+        if "SWITCH" in device_type and "child_device" in components:
+            return DeviceType.WallSwitch
         if "dimmer_calibration" in components:
             return DeviceType.Dimmer
         if "brightness" in components:

diff --git a/kasa/tests/device_fixtures.py b/kasa/tests/device_fixtures.py
@@ -92,6 +92,7 @@
 SWITCHES_SMART = {
     "KS205",
     "KS225",
+    "KS240",
     "S500D",
     "S505",
 }

diff --git a/kasa/tests/fakeprotocol_smart.py b/kasa/tests/fakeprotocol_smart.py
@@ -139,10 +139,29 @@ def _handle_control_child(self, params: dict):
 
         # We only support get & set device info for now.
         if child_method == "get_device_info":
-            return {"result": info, "error_code": 0}
+            result = copy.deepcopy(info)
+            return {"result": result, "error_code": 0}
         elif child_method == "set_device_info":
             info.update(child_params)
             return {"error_code": 0}
+        elif (
+            # FIXTURE_MISSING is for service calls not in place when
+            # SMART fixtures started to be generated
+            missing_result := self.FIXTURE_MISSING_MAP.get(child_method)
+        ) and missing_result[0] in self.components:
+            result = copy.deepcopy(missing_result[1])
+            retval = {"result": result, "error_code": 0}
+            return retval
+        else:
+            # PARAMS error returned for KS240 when get_device_usage called
+            # on parent device.  Could be any error code though.
+            # TODO: Try to figure out if there's a way to prevent the KS240 smartdevice
+            # calling the unsupported device in the first place.
+            retval = {
+                "error_code": SmartErrorCode.PARAMS_ERROR.value,
+                "method": child_method,
+            }
+            return retval
 
         raise NotImplementedError(
             "Method %s not implemented for children" % child_method