diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 500f21bb..b5f5ae62 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -8,6 +8,35 @@ Unreleased
 **BREAKING CHANGES**: Public API surface trimmed and dead code removed.
 These changes require a major version bump.
 
+Modernization (Python 3.14)
+---------------------------
+- **Removed** ``from __future__ import annotations`` **project-wide**
+  (57 files): redundant on a Python >=3.14-only package where lazy
+  annotation evaluation (PEP 649) is the default.
+- **Adopted additional ruff rule sets**: ``RUF`` (Ruff-specific),
+  ``DTZ`` (naive datetime), ``PTH`` (pathlib), ``ASYNC``, and ``PERF``,
+  with documented ignores for intentional patterns (grouped ``__all__``
+  lists, unicode degree signs, public ``timeout`` parameters). Fixes
+  applied for all resulting findings, including a timezone-naive
+  timestamp in CSV exports (now timezone-aware local time),
+  ``Path.open()`` usage, ``itertools.pairwise()`` in the CLI range
+  collapser, a ``ClassVar`` annotation on the capability map, and
+  dangling ``asyncio.create_task`` references in tests.
+- **PeriodicRequestType is now a StrEnum** (was a plain ``Enum`` with
+  string values), matching the enum style used elsewhere.
+- **Event payload dataclasses use** ``slots=True``: the frozen event
+  dataclasses in ``mqtt_events.py`` and ``events.EventListener`` are
+  created per state change; slots reduce their memory footprint.
+- **match statement** for the periodic request-type dispatch.
+
+Testing
+-------
+- New unit tests for previously untested modules:
+  ``topic_builder.py`` (full topic schema), ``field_factory.py``
+  (metadata defaults, overrides, merge semantics), and
+  ``models/_converters.py`` (unit-preference conversions and
+  round-trips).
+
 Removed
 -------
 - **Deprecated ``.control`` property**: removed
diff --git a/examples/advanced/mqtt_diagnostics.py b/examples/advanced/mqtt_diagnostics.py
index 5a96d8b9..cd4eed69 100755
--- a/examples/advanced/mqtt_diagnostics.py
+++ b/examples/advanced/mqtt_diagnostics.py
@@ -84,7 +84,7 @@ async def export_diagnostics(self, interval: float = 300.0) -> None:
                 output_file = self.output_dir / f"diagnostics_{timestamp}.json"
 
                 json_data = self.diagnostics.export_json()
-                with open(output_file, "w") as f:
+                with output_file.open("w") as f:
                     f.write(json_data)
 
                 _logger.info(f"Exported diagnostics to {output_file}")
@@ -276,7 +276,7 @@ async def run_example(
                     _logger.info("Exporting final diagnostics...")
                     timestamp = datetime.now(UTC).strftime("%Y%m%d_%H%M%S")
                     final_file = self.output_dir / f"diagnostics_final_{timestamp}.json"
-                    with open(final_file, "w") as f:
+                    with final_file.open("w") as f:
                         f.write(self.diagnostics.export_json())
                     _logger.info(f"Final diagnostics saved to {final_file}")
 
diff --git a/examples/mask.py b/examples/mask.py
index 94628f57..60685469 100644
--- a/examples/mask.py
+++ b/examples/mask.py
@@ -4,8 +4,6 @@
 these helpers; if that import fails we leave a small fallback in each script.
 """
 
-from __future__ import annotations
-
 import re
 
 
diff --git a/pyproject.toml b/pyproject.toml
index 5f056eab..37c1052f 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -57,11 +57,30 @@ select = [
     "C4",    # flake8-comprehensions
     "SIM",   # flake8-simplify
     "S",     # flake8-bandit (security)
+    "RUF",   # Ruff-specific rules (incl. unused noqa)
+    "DTZ",   # flake8-datetimez (naive datetime usage)
+    "PTH",   # flake8-use-pathlib
+    "ASYNC", # flake8-async
+    "PERF",  # perflint
 ]
 
 ignore = [
     "E203",  # whitespace before ':' (conflicts with black/ruff format)
     "B904",  # raise from - will be addressed in a future update
+    # Async functions taking a `timeout:` parameter are a deliberate,
+    # documented public API of this library (e.g. wait_for, command
+    # helpers); switching callers to asyncio.timeout() would be a
+    # breaking change with no behavioral benefit.
+    "ASYNC109",
+    # Degree signs, en-dashes, and multiplication signs in docstrings
+    # and user-facing strings are intentional (temperature units,
+    # ranges), not typos of ASCII look-alikes.
+    "RUF001",
+    "RUF002",
+    "RUF003",
+    # __all__ lists are deliberately grouped by category with comments,
+    # not sorted alphabetically.
+    "RUF022",
 ]
 
 # Allow autofix for all enabled rules (when `--fix` is provided)
diff --git a/src/nwp500/__init__.py b/src/nwp500/__init__.py
index 01ce3925..0a0b0812 100644
--- a/src/nwp500/__init__.py
+++ b/src/nwp500/__init__.py
@@ -4,8 +4,6 @@
 communication for NWP500 heat pump water heaters.
 """
 
-from __future__ import annotations
-
 from importlib.metadata import (
     PackageNotFoundError,
     version,
diff --git a/src/nwp500/_base.py b/src/nwp500/_base.py
index faa06742..298aea28 100644
--- a/src/nwp500/_base.py
+++ b/src/nwp500/_base.py
@@ -5,8 +5,6 @@
 protocol models share a single base class.
 """
 
-from __future__ import annotations
-
 from typing import Any
 
 from pydantic import BaseModel, ConfigDict
diff --git a/src/nwp500/api_client.py b/src/nwp500/api_client.py
index b55c187e..c48f7651 100644
--- a/src/nwp500/api_client.py
+++ b/src/nwp500/api_client.py
@@ -4,8 +4,6 @@
 This module provides an async HTTP client for device management and control.
 """
 
-from __future__ import annotations
-
 import logging
 from typing import Any, Self
 
@@ -231,7 +229,7 @@ async def _make_request(
 
         except aiohttp.ClientError as e:
             _logger.error(f"Network error: {e}")
-            raise APIError(f"Network error: {str(e)}") from e
+            raise APIError(f"Network error: {e!s}") from e
 
     # Device Management Endpoints
 
diff --git a/src/nwp500/auth.py b/src/nwp500/auth.py
index 84dab355..e38916c8 100644
--- a/src/nwp500/auth.py
+++ b/src/nwp500/auth.py
@@ -11,8 +11,6 @@
 4. Refresh tokens when accessToken expires
 """
 
-from __future__ import annotations
-
 import asyncio
 import json
 import logging
@@ -506,14 +504,12 @@ async def sign_in(
         except aiohttp.ClientError as e:
             _logger.error(f"Network error during sign-in: {e}")
             raise AuthenticationError(
-                f"Network error: {str(e)}",
+                f"Network error: {e!s}",
                 retriable=True,
             ) from e
         except (KeyError, ValueError, json.JSONDecodeError) as e:
             _logger.error(f"Failed to parse authentication response: {e}")
-            raise AuthenticationError(
-                f"Invalid response format: {str(e)}"
-            ) from e
+            raise AuthenticationError(f"Invalid response format: {e!s}") from e
 
     async def refresh_token(
         self, refresh_token: str | None = None
@@ -641,12 +637,12 @@ async def _refresh_token_unlocked(
         except aiohttp.ClientError as e:
             _logger.error(f"Network error during token refresh: {e}")
             raise TokenRefreshError(
-                f"Network error: {str(e)}",
+                f"Network error: {e!s}",
                 retriable=True,
             ) from e
         except (KeyError, ValueError, json.JSONDecodeError) as e:
             _logger.error(f"Failed to parse refresh response: {e}")
-            raise TokenRefreshError(f"Invalid response format: {str(e)}") from e
+            raise TokenRefreshError(f"Invalid response format: {e!s}") from e
 
     async def re_authenticate(self) -> AuthenticationResponse:
         """
diff --git a/src/nwp500/cli/__init__.py b/src/nwp500/cli/__init__.py
index 62ad37c2..ca5d6239 100644
--- a/src/nwp500/cli/__init__.py
+++ b/src/nwp500/cli/__init__.py
@@ -1,7 +1,5 @@
 """CLI package for nwp500-python."""
 
-from __future__ import annotations
-
 from .__main__ import run
 from .handlers import (
     handle_device_info_request,
diff --git a/src/nwp500/cli/__main__.py b/src/nwp500/cli/__main__.py
index 21c584ba..7d6c7fae 100644
--- a/src/nwp500/cli/__main__.py
+++ b/src/nwp500/cli/__main__.py
@@ -1,7 +1,5 @@
 """Navien Water Heater Control CLI - Main Entry Point."""
 
-from __future__ import annotations
-
 import asyncio
 import functools
 import logging
diff --git a/src/nwp500/cli/handlers.py b/src/nwp500/cli/handlers.py
index c94b0449..3bcc2e3d 100644
--- a/src/nwp500/cli/handlers.py
+++ b/src/nwp500/cli/handlers.py
@@ -1,7 +1,5 @@
 """Command handlers for CLI operations."""
 
-from __future__ import annotations
-
 import asyncio
 import json
 import logging
diff --git a/src/nwp500/cli/monitoring.py b/src/nwp500/cli/monitoring.py
index 51c90868..37128197 100644
--- a/src/nwp500/cli/monitoring.py
+++ b/src/nwp500/cli/monitoring.py
@@ -1,7 +1,5 @@
 """Monitoring and periodic status polling."""
 
-from __future__ import annotations
-
 import asyncio
 import logging
 
diff --git a/src/nwp500/cli/output_formatters.py b/src/nwp500/cli/output_formatters.py
index 5652fd7f..bb5fde53 100644
--- a/src/nwp500/cli/output_formatters.py
+++ b/src/nwp500/cli/output_formatters.py
@@ -1,7 +1,5 @@
 """Output formatting utilities for CLI (CSV, JSON)."""
 
-from __future__ import annotations
-
 import csv
 import json
 import logging
@@ -369,13 +367,14 @@ def write_status_to_csv(file_path: str, status: DeviceStatus) -> None:
         # Convert status to dict (enums are already converted to names)
         status_dict = status.model_dump()
 
-        # Add a timestamp to the beginning of the data
-        status_dict["timestamp"] = datetime.now().isoformat()
+        # Add a timestamp to the beginning of the data (timezone-aware,
+        # in the local timezone)
+        status_dict["timestamp"] = datetime.now().astimezone().isoformat()
 
         # Check if file exists to determine if we need to write the header
         file_exists = Path(file_path).exists()
 
-        with open(file_path, "a", newline="") as csvfile:
+        with Path(file_path).open("a", newline="") as csvfile:
             # Get the field names from the dict keys
             fieldnames = list(status_dict.keys())
             writer = csv.DictWriter(csvfile, fieldnames=fieldnames)
diff --git a/src/nwp500/cli/rich_output.py b/src/nwp500/cli/rich_output.py
index c9099f3c..fed9d21c 100644
--- a/src/nwp500/cli/rich_output.py
+++ b/src/nwp500/cli/rich_output.py
@@ -1,7 +1,6 @@
 """Rich-enhanced output formatting with graceful fallback."""
 
-from __future__ import annotations
-
+import itertools
 import json
 import logging
 import os
@@ -142,7 +141,7 @@ def _collapse_ranges(
 
     # Build groups of consecutive items
     groups: list[list[Any]] = [[items[0]]]
-    for prev, curr in zip(items, items[1:], strict=False):
+    for prev, curr in itertools.pairwise(items):
         if isinstance(prev, int):
             consecutive = (curr - prev) == 1 or (
                 prev == cycle_size and curr == 1
diff --git a/src/nwp500/cli/token_storage.py b/src/nwp500/cli/token_storage.py
index 6bb2a489..7bdfcaad 100644
--- a/src/nwp500/cli/token_storage.py
+++ b/src/nwp500/cli/token_storage.py
@@ -1,7 +1,5 @@
 """Token storage and management for CLI authentication."""
 
-from __future__ import annotations
-
 import json
 import logging
 import os
@@ -47,7 +45,7 @@ def load_tokens() -> tuple[AuthTokens | None, str | None]:
     if not TOKEN_FILE.exists():
         return None, None
     try:
-        with open(TOKEN_FILE) as f:
+        with TOKEN_FILE.open() as f:
             data = json.load(f)
             email = data.get("email")
             if not email:
diff --git a/src/nwp500/command_decorators.py b/src/nwp500/command_decorators.py
index 56ee072b..fbc28843 100644
--- a/src/nwp500/command_decorators.py
+++ b/src/nwp500/command_decorators.py
@@ -4,8 +4,6 @@
 before command execution, preventing unsupported commands from being sent.
 """
 
-from __future__ import annotations
-
 import functools
 import inspect
 import logging
@@ -84,7 +82,7 @@ async def async_wrapper(
                     # Wrap other errors (timeouts, connection issues, etc)
                     raise DeviceCapabilityError(
                         feature,
-                        f"Cannot execute {func.__name__}: {str(e)}",
+                        f"Cannot execute {func.__name__}: {e!s}",
                     ) from e
 
                 if cached_features is None:
diff --git a/src/nwp500/config.py b/src/nwp500/config.py
index fa22ad77..97d825da 100644
--- a/src/nwp500/config.py
+++ b/src/nwp500/config.py
@@ -1,7 +1,5 @@
 """Configuration for the Navien API client."""
 
-from __future__ import annotations
-
 API_BASE_URL = "https://nlus.naviensmartcontrol.com/api/v2.1"
 SIGN_IN_ENDPOINT = "/user/sign-in"
 REFRESH_ENDPOINT = "/auth/refresh"
diff --git a/src/nwp500/converters.py b/src/nwp500/converters.py
index d9ec1167..01dec4ee 100644
--- a/src/nwp500/converters.py
+++ b/src/nwp500/converters.py
@@ -7,8 +7,6 @@
 See docs/protocol/quick_reference.rst for comprehensive protocol details.
 """
 
-from __future__ import annotations
-
 from collections.abc import Callable
 from typing import Any
 
diff --git a/src/nwp500/device_capabilities.py b/src/nwp500/device_capabilities.py
index d907ddf1..088a8204 100644
--- a/src/nwp500/device_capabilities.py
+++ b/src/nwp500/device_capabilities.py
@@ -6,10 +6,8 @@
 individual checker functions.
 """
 
-from __future__ import annotations
-
 from collections.abc import Callable
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, ClassVar
 
 from .exceptions import DeviceCapabilityError
 
@@ -34,7 +32,7 @@ class MqttDeviceCapabilityChecker:
     # Map of controllable features to their check functions
     # Capability names MUST match DeviceFeature attribute names exactly
     # for traceability: capability name -> DeviceFeature.{name}
-    _CAPABILITY_MAP: dict[str, CapabilityCheckFn] = {
+    _CAPABILITY_MAP: ClassVar[dict[str, CapabilityCheckFn]] = {
         "power_use": lambda f: bool(f.power_use),
         "dhw_use": lambda f: bool(f.dhw_use),
         "dhw_temperature_setting_use": lambda f: _check_dhw_temperature_control(
diff --git a/src/nwp500/device_info_cache.py b/src/nwp500/device_info_cache.py
index a1f5865c..4d3e3b43 100644
--- a/src/nwp500/device_info_cache.py
+++ b/src/nwp500/device_info_cache.py
@@ -4,8 +4,6 @@
 with automatic periodic updates to keep data synchronized with the device.
 """
 
-from __future__ import annotations
-
 import asyncio
 import logging
 from datetime import UTC, datetime, timedelta
diff --git a/src/nwp500/encoding.py b/src/nwp500/encoding.py
index 85203270..c7f75165 100644
--- a/src/nwp500/encoding.py
+++ b/src/nwp500/encoding.py
@@ -6,8 +6,6 @@
 These utilities are used by both the API client and MQTT client.
 """
 
-from __future__ import annotations
-
 import logging
 from collections.abc import Iterable
 from decimal import ROUND_HALF_UP, Decimal
diff --git a/src/nwp500/enums.py b/src/nwp500/enums.py
index 7899f074..ae726672 100644
--- a/src/nwp500/enums.py
+++ b/src/nwp500/enums.py
@@ -7,8 +7,6 @@
 See docs/protocol/quick_reference.rst for comprehensive protocol details.
 """
 
-from __future__ import annotations
-
 from enum import IntEnum, StrEnum
 
 # ============================================================================
diff --git a/src/nwp500/events.py b/src/nwp500/events.py
index c061f39f..b4d0ed43 100644
--- a/src/nwp500/events.py
+++ b/src/nwp500/events.py
@@ -6,8 +6,6 @@
 detection.
 """
 
-from __future__ import annotations
-
 import asyncio
 import inspect
 import logging
@@ -23,7 +21,7 @@
 _logger = logging.getLogger(__name__)
 
 
-@dataclass(frozen=True)
+@dataclass(frozen=True, slots=True)
 class EventListener:
     """Represents a registered event listener."""
 
diff --git a/src/nwp500/exceptions.py b/src/nwp500/exceptions.py
index ab861efd..c6a57d91 100644
--- a/src/nwp500/exceptions.py
+++ b/src/nwp500/exceptions.py
@@ -60,8 +60,6 @@
         # handle other validation errors
 """
 
-from __future__ import annotations
-
 from typing import Any
 
 __author__ = "Emmanuel Levijarvi"
diff --git a/src/nwp500/factory.py b/src/nwp500/factory.py
index 48526262..378b2bd2 100644
--- a/src/nwp500/factory.py
+++ b/src/nwp500/factory.py
@@ -18,8 +18,6 @@
     ...     devices = await api.list_devices()
 """
 
-from __future__ import annotations
-
 import asyncio
 
 from .api_client import NavienAPIClient
diff --git a/src/nwp500/field_factory.py b/src/nwp500/field_factory.py
index 234e9b3f..51e9498c 100644
--- a/src/nwp500/field_factory.py
+++ b/src/nwp500/field_factory.py
@@ -20,8 +20,6 @@
     ...     temp: float = temperature_field("DHW Temperature", unit="°F")
 """
 
-from __future__ import annotations
-
 from typing import Any, cast
 
 from pydantic import Field
diff --git a/src/nwp500/models/__init__.py b/src/nwp500/models/__init__.py
index e23c9cac..2311709e 100644
--- a/src/nwp500/models/__init__.py
+++ b/src/nwp500/models/__init__.py
@@ -6,8 +6,6 @@
 These models are based on the MQTT message formats and API responses.
 """
 
-from __future__ import annotations
-
 from .._base import NavienBaseModel
 from ._converters import (
     fahrenheit_to_half_celsius,
diff --git a/src/nwp500/models/_converters.py b/src/nwp500/models/_converters.py
index b24b572f..c19eae97 100644
--- a/src/nwp500/models/_converters.py
+++ b/src/nwp500/models/_converters.py
@@ -1,5 +1,3 @@
-from __future__ import annotations
-
 from ..temperature import HalfCelsius
 from ..unit_system import get_unit_system
 
diff --git a/src/nwp500/models/device.py b/src/nwp500/models/device.py
index ae7a501f..3538743f 100644
--- a/src/nwp500/models/device.py
+++ b/src/nwp500/models/device.py
@@ -1,5 +1,3 @@
-from __future__ import annotations
-
 from typing import Annotated, Self
 
 from pydantic import BeforeValidator
diff --git a/src/nwp500/models/energy.py b/src/nwp500/models/energy.py
index d2410bfa..9d3801a7 100644
--- a/src/nwp500/models/energy.py
+++ b/src/nwp500/models/energy.py
@@ -1,5 +1,3 @@
-from __future__ import annotations
-
 from pydantic import Field
 
 from .._base import NavienBaseModel
diff --git a/src/nwp500/models/feature.py b/src/nwp500/models/feature.py
index 0dc56094..36bd7d7a 100644
--- a/src/nwp500/models/feature.py
+++ b/src/nwp500/models/feature.py
@@ -1,5 +1,3 @@
-from __future__ import annotations
-
 from typing import Annotated
 
 from pydantic import BeforeValidator, Field, computed_field
diff --git a/src/nwp500/models/mqtt_models.py b/src/nwp500/models/mqtt_models.py
index 151d38f2..50068b97 100644
--- a/src/nwp500/models/mqtt_models.py
+++ b/src/nwp500/models/mqtt_models.py
@@ -1,5 +1,3 @@
-from __future__ import annotations
-
 from typing import Any
 
 from pydantic import Field
diff --git a/src/nwp500/models/schedule.py b/src/nwp500/models/schedule.py
index 7666d7f4..6483dcb7 100644
--- a/src/nwp500/models/schedule.py
+++ b/src/nwp500/models/schedule.py
@@ -1,5 +1,3 @@
-from __future__ import annotations
-
 from typing import Any, cast
 
 from pydantic import ConfigDict, Field, computed_field, model_validator
diff --git a/src/nwp500/models/status.py b/src/nwp500/models/status.py
index d436d608..7865693f 100644
--- a/src/nwp500/models/status.py
+++ b/src/nwp500/models/status.py
@@ -1,5 +1,3 @@
-from __future__ import annotations
-
 from typing import Annotated
 
 from pydantic import BeforeValidator, Field, computed_field
diff --git a/src/nwp500/models/tou.py b/src/nwp500/models/tou.py
index 5f858856..65009e66 100644
--- a/src/nwp500/models/tou.py
+++ b/src/nwp500/models/tou.py
@@ -1,5 +1,3 @@
-from __future__ import annotations
-
 from typing import Any, cast
 
 from pydantic import ConfigDict, Field, computed_field, model_validator
diff --git a/src/nwp500/mqtt/__init__.py b/src/nwp500/mqtt/__init__.py
index 2a82fd3a..2a0d2058 100644
--- a/src/nwp500/mqtt/__init__.py
+++ b/src/nwp500/mqtt/__init__.py
@@ -11,8 +11,6 @@
 - MqttMetrics, ConnectionDropEvent, ConnectionEvent: Diagnostic types
 """
 
-from __future__ import annotations
-
 from .client import NavienMqttClient
 from .diagnostics import (
     ConnectionDropEvent,
diff --git a/src/nwp500/mqtt/client.py b/src/nwp500/mqtt/client.py
index 938bac51..218bdf8a 100644
--- a/src/nwp500/mqtt/client.py
+++ b/src/nwp500/mqtt/client.py
@@ -9,8 +9,6 @@
 the authentication flow.
 """
 
-from __future__ import annotations
-
 import asyncio
 import concurrent.futures
 import logging
diff --git a/src/nwp500/mqtt/command_queue.py b/src/nwp500/mqtt/command_queue.py
index cf88eca5..cd918759 100644
--- a/src/nwp500/mqtt/command_queue.py
+++ b/src/nwp500/mqtt/command_queue.py
@@ -5,8 +5,6 @@
 and automatically sends them when the connection is restored.
 """
 
-from __future__ import annotations
-
 import logging
 from collections import deque
 from collections.abc import Callable
diff --git a/src/nwp500/mqtt/connection.py b/src/nwp500/mqtt/connection.py
index 61d2af5d..2bc3f4f4 100644
--- a/src/nwp500/mqtt/connection.py
+++ b/src/nwp500/mqtt/connection.py
@@ -6,8 +6,6 @@
 including credential management and connection state tracking.
 """
 
-from __future__ import annotations
-
 import asyncio
 import concurrent.futures
 import json
diff --git a/src/nwp500/mqtt/control.py b/src/nwp500/mqtt/control.py
index 038abdd7..79d82ff3 100644
--- a/src/nwp500/mqtt/control.py
+++ b/src/nwp500/mqtt/control.py
@@ -17,8 +17,6 @@
 - Recirculation pump control and scheduling
 """
 
-from __future__ import annotations
-
 import logging
 from collections.abc import Awaitable, Callable, Sequence
 from datetime import UTC, datetime
diff --git a/src/nwp500/mqtt/diagnostics.py b/src/nwp500/mqtt/diagnostics.py
index 4df6a328..dc0c0c55 100644
--- a/src/nwp500/mqtt/diagnostics.py
+++ b/src/nwp500/mqtt/diagnostics.py
@@ -8,8 +8,6 @@
 - Client-side configuration issues (insufficient keep-alive, poor backoff)
 """
 
-from __future__ import annotations
-
 import json
 import logging
 import time
diff --git a/src/nwp500/mqtt/periodic.py b/src/nwp500/mqtt/periodic.py
index 7ead5186..537eacfd 100644
--- a/src/nwp500/mqtt/periodic.py
+++ b/src/nwp500/mqtt/periodic.py
@@ -9,8 +9,6 @@
 - Per-device, per-type task management
 """
 
-from __future__ import annotations
-
 import asyncio
 import contextlib
 import logging
@@ -170,10 +168,11 @@ async def periodic_request() -> None:
                             consecutive_skips = 0
 
                         # Send appropriate request type
-                        if request_type == PeriodicRequestType.DEVICE_INFO:
-                            await self._request_device_info(device)
-                        elif request_type == PeriodicRequestType.DEVICE_STATUS:
-                            await self._request_device_status(device)
+                        match request_type:
+                            case PeriodicRequestType.DEVICE_INFO:
+                                await self._request_device_info(device)
+                            case PeriodicRequestType.DEVICE_STATUS:
+                                await self._request_device_status(device)
 
                         _logger.debug(
                             "Sent periodic %s request for %s",
diff --git a/src/nwp500/mqtt/reconnection.py b/src/nwp500/mqtt/reconnection.py
index 732902ee..89919b1c 100644
--- a/src/nwp500/mqtt/reconnection.py
+++ b/src/nwp500/mqtt/reconnection.py
@@ -5,8 +5,6 @@
 the MQTT connection is interrupted.
 """
 
-from __future__ import annotations
-
 import asyncio
 import contextlib
 import logging
diff --git a/src/nwp500/mqtt/state_tracker.py b/src/nwp500/mqtt/state_tracker.py
index ea7e8a40..f0446d3f 100644
--- a/src/nwp500/mqtt/state_tracker.py
+++ b/src/nwp500/mqtt/state_tracker.py
@@ -5,8 +5,6 @@
 errors).
 """
 
-from __future__ import annotations
-
 import logging
 
 from ..events import EventEmitter
diff --git a/src/nwp500/mqtt/subscriptions.py b/src/nwp500/mqtt/subscriptions.py
index 6ab0cb38..b64ce165 100644
--- a/src/nwp500/mqtt/subscriptions.py
+++ b/src/nwp500/mqtt/subscriptions.py
@@ -9,8 +9,6 @@
 - State change detection and event emission
 """
 
-from __future__ import annotations
-
 import asyncio
 import json
 import logging
diff --git a/src/nwp500/mqtt/utils.py b/src/nwp500/mqtt/utils.py
index 12f75698..91fc46a0 100644
--- a/src/nwp500/mqtt/utils.py
+++ b/src/nwp500/mqtt/utils.py
@@ -5,13 +5,11 @@
 configuration classes, and common data structures used across MQTT modules.
 """
 
-from __future__ import annotations
-
 import re
 import uuid
 from dataclasses import dataclass
 from datetime import datetime
-from enum import Enum
+from enum import StrEnum
 from typing import Any
 
 from awscrt import mqtt
@@ -292,7 +290,7 @@ class QueuedCommand:
     timestamp: datetime
 
 
-class PeriodicRequestType(Enum):
+class PeriodicRequestType(StrEnum):
     """Types of periodic requests that can be sent.
 
     Attributes:
diff --git a/src/nwp500/mqtt_events.py b/src/nwp500/mqtt_events.py
index bdd6257c..53c3e735 100644
--- a/src/nwp500/mqtt_events.py
+++ b/src/nwp500/mqtt_events.py
@@ -28,8 +28,6 @@ def on_temperature_changed(event):
         print(event_name)
 """
 
-from __future__ import annotations
-
 from dataclasses import dataclass
 from typing import TYPE_CHECKING, cast
 
@@ -38,7 +36,7 @@ def on_temperature_changed(event):
     from .models import DeviceFeature, DeviceStatus
 
 
-@dataclass(frozen=True)
+@dataclass(frozen=True, slots=True)
 class ConnectionInterruptedEvent:
     """Emitted when MQTT connection is interrupted.
 
@@ -49,7 +47,7 @@ class ConnectionInterruptedEvent:
     error: Exception
 
 
-@dataclass(frozen=True)
+@dataclass(frozen=True, slots=True)
 class ConnectionResumedEvent:
     """Emitted when MQTT connection is resumed after interruption.
 
@@ -62,7 +60,7 @@ class ConnectionResumedEvent:
     session_present: bool
 
 
-@dataclass(frozen=True)
+@dataclass(frozen=True, slots=True)
 class StatusReceivedEvent:
     """Emitted when a device status message is received.
 
@@ -75,7 +73,7 @@ class StatusReceivedEvent:
     status: DeviceStatus
 
 
-@dataclass(frozen=True)
+@dataclass(frozen=True, slots=True)
 class TemperatureChangedEvent:
     """Emitted when the DHW temperature changes.
 
@@ -92,7 +90,7 @@ class TemperatureChangedEvent:
     new_temperature: float
 
 
-@dataclass(frozen=True)
+@dataclass(frozen=True, slots=True)
 class ModeChangedEvent:
     """Emitted when the device operation mode changes.
 
@@ -107,7 +105,7 @@ class ModeChangedEvent:
     new_mode: CurrentOperationMode
 
 
-@dataclass(frozen=True)
+@dataclass(frozen=True, slots=True)
 class PowerChangedEvent:
     """Emitted when instantaneous power consumption changes.
 
@@ -122,7 +120,7 @@ class PowerChangedEvent:
     new_power: float
 
 
-@dataclass(frozen=True)
+@dataclass(frozen=True, slots=True)
 class HeatingStartedEvent:
     """Emitted when device transitions from idle to heating.
 
@@ -135,7 +133,7 @@ class HeatingStartedEvent:
     status: DeviceStatus
 
 
-@dataclass(frozen=True)
+@dataclass(frozen=True, slots=True)
 class HeatingStoppedEvent:
     """Emitted when device transitions from heating to idle.
 
@@ -148,7 +146,7 @@ class HeatingStoppedEvent:
     status: DeviceStatus
 
 
-@dataclass(frozen=True)
+@dataclass(frozen=True, slots=True)
 class ErrorDetectedEvent:
     """Emitted when a device error is first detected.
 
@@ -163,7 +161,7 @@ class ErrorDetectedEvent:
     status: DeviceStatus
 
 
-@dataclass(frozen=True)
+@dataclass(frozen=True, slots=True)
 class ErrorClearedEvent:
     """Emitted when a device error is resolved.
 
@@ -176,7 +174,7 @@ class ErrorClearedEvent:
     error_code: ErrorCode
 
 
-@dataclass(frozen=True)
+@dataclass(frozen=True, slots=True)
 class FeatureReceivedEvent:
     """Emitted when device feature information is received.
 
diff --git a/src/nwp500/openei.py b/src/nwp500/openei.py
index 827af8dc..d7485553 100644
--- a/src/nwp500/openei.py
+++ b/src/nwp500/openei.py
@@ -8,8 +8,6 @@
 API key can be obtained for free at https://openei.org/services/api/signup/
 """
 
-from __future__ import annotations
-
 import logging
 import os
 from typing import Any
diff --git a/src/nwp500/reservations.py b/src/nwp500/reservations.py
index 5dd6172e..28bbe455 100644
--- a/src/nwp500/reservations.py
+++ b/src/nwp500/reservations.py
@@ -9,8 +9,6 @@
 All functions are ``async`` and require a connected :class:`NavienMqttClient`.
 """
 
-from __future__ import annotations
-
 import asyncio
 import logging
 from collections.abc import Sequence
diff --git a/src/nwp500/temperature.py b/src/nwp500/temperature.py
index d7276cac..0e043f5e 100644
--- a/src/nwp500/temperature.py
+++ b/src/nwp500/temperature.py
@@ -7,8 +7,6 @@
 All values are converted to preferred unit based on device preference.
 """
 
-from __future__ import annotations
-
 import math
 from typing import ClassVar, Self
 
diff --git a/src/nwp500/topic_builder.py b/src/nwp500/topic_builder.py
index 41d92596..b9a5677a 100644
--- a/src/nwp500/topic_builder.py
+++ b/src/nwp500/topic_builder.py
@@ -12,8 +12,6 @@
   Event:                        evt/{device_type}/navilink-{mac}/{suffix}
 """
 
-from __future__ import annotations
-
 
 class MqttTopicBuilder:
     """Helper to construct standard MQTT topics for Navien devices."""
diff --git a/src/nwp500/unit_system.py b/src/nwp500/unit_system.py
index 721311cf..0e0770ea 100644
--- a/src/nwp500/unit_system.py
+++ b/src/nwp500/unit_system.py
@@ -11,8 +11,6 @@
 run outside the task that configured it.
 """
 
-from __future__ import annotations
-
 import logging
 from typing import Literal
 
diff --git a/src/nwp500/utils.py b/src/nwp500/utils.py
index 964db2e1..5f1be094 100644
--- a/src/nwp500/utils.py
+++ b/src/nwp500/utils.py
@@ -5,8 +5,6 @@
 including performance monitoring decorators and helper functions.
 """
 
-from __future__ import annotations
-
 import functools
 import inspect
 import logging
diff --git a/tests/test_bug_fixes.py b/tests/test_bug_fixes.py
index 08765eae..656cdfbe 100644
--- a/tests/test_bug_fixes.py
+++ b/tests/test_bug_fixes.py
@@ -1,7 +1,5 @@
 """Tests for bug fixes: diagnostics, config validation, encoding, cache."""
 
-from __future__ import annotations
-
 import asyncio
 import json
 from unittest.mock import patch
@@ -97,8 +95,9 @@ async def emit_soon():
             await asyncio.sleep(0.01)
             await emitter.emit("test_event", "data")
 
-        asyncio.create_task(emit_soon())
+        task = asyncio.create_task(emit_soon())
         result = await emitter.wait_for("test_event", timeout=1.0)
+        await task
         assert result == ("data",)
 
 
diff --git a/tests/test_events.py b/tests/test_events.py
index ca50e2e9..03bd1ee1 100644
--- a/tests/test_events.py
+++ b/tests/test_events.py
@@ -245,10 +245,11 @@ async def emit_later():
         await emitter.emit("test_event", "test_value")
 
     # Start emitting in background
-    asyncio.create_task(emit_later())
+    task = asyncio.create_task(emit_later())
 
     # Wait for event
     result = await emitter.wait_for("test_event", timeout=1.0)
+    await task
 
     assert result == ("test_value",)
 
diff --git a/tests/test_mqtt_clean_session_resume.py b/tests/test_mqtt_clean_session_resume.py
index cb92a714..80df6016 100644
--- a/tests/test_mqtt_clean_session_resume.py
+++ b/tests/test_mqtt_clean_session_resume.py
@@ -1,7 +1,5 @@
 """Tests for MQTT client clean session reconnection handling."""
 
-from __future__ import annotations
-
 from unittest.mock import AsyncMock, MagicMock, patch
 
 import pytest
diff --git a/tests/test_mqtt_reconnection.py b/tests/test_mqtt_reconnection.py
index d5f0382f..45ca4eee 100644
--- a/tests/test_mqtt_reconnection.py
+++ b/tests/test_mqtt_reconnection.py
@@ -1,7 +1,5 @@
 """Tests for MQTT reconnection: old connection cleanup."""
 
-from __future__ import annotations
-
 import concurrent.futures
 from unittest.mock import MagicMock
 
diff --git a/tests/test_mqtt_reconnection_storm.py b/tests/test_mqtt_reconnection_storm.py
index 3b734825..ae4cb026 100644
--- a/tests/test_mqtt_reconnection_storm.py
+++ b/tests/test_mqtt_reconnection_storm.py
@@ -35,8 +35,6 @@
   Task operations are safe.
 """
 
-from __future__ import annotations
-
 import asyncio
 from unittest.mock import AsyncMock, MagicMock, patch
 
@@ -397,7 +395,7 @@ def test_actively_reconnecting_initialises_false(self):
         assert client._actively_reconnecting is False
 
     @pytest.mark.asyncio(loop_scope="function")
-    async def test_interrupted_internal_skips_handler_when_flag_set(  # noqa: E501
+    async def test_interrupted_internal_skips_handler_when_flag_set(
         self,
     ):
         """
diff --git a/tests/test_multi_device.py b/tests/test_multi_device.py
index f48101cd..e681a74b 100644
--- a/tests/test_multi_device.py
+++ b/tests/test_multi_device.py
@@ -75,7 +75,7 @@ async def test_state_tracker_emits_with_mac():
     await tracker.process(mac1, status1_v2)
     assert emitter.emit.call_count == 1
 
-    args, kwargs = emitter.emit.call_args
+    args, _kwargs = emitter.emit.call_args
     assert args[0] == "temperature_changed"
     event = args[1]
     assert isinstance(event, TemperatureChangedEvent)
@@ -100,7 +100,7 @@ async def test_state_tracker_emits_with_mac():
 
     # Should have emitted another event for mac2
     assert emitter.emit.call_count == 2
-    args, kwargs = emitter.emit.call_args
+    args, _kwargs = emitter.emit.call_args
     event = args[1]
     assert event.device_mac == mac2
 
diff --git a/tests/test_protocol_correctness.py b/tests/test_protocol_correctness.py
index 3c8c67b3..b5b89143 100644
--- a/tests/test_protocol_correctness.py
+++ b/tests/test_protocol_correctness.py
@@ -10,8 +10,6 @@
 - TOU price encoding (half-up rounding, bool rejection)
 """
 
-from __future__ import annotations
-
 from datetime import UTC, datetime, timedelta
 from unittest.mock import AsyncMock, MagicMock
 
diff --git a/tests/test_public_api.py b/tests/test_public_api.py
index e6438f9e..6dd02b6d 100644
--- a/tests/test_public_api.py
+++ b/tests/test_public_api.py
@@ -1,7 +1,5 @@
 """Tests for the public API surface of the nwp500 package."""
 
-from __future__ import annotations
-
 import nwp500
 
 
diff --git a/tests/test_reservations.py b/tests/test_reservations.py
index de155012..45bc5b76 100644
--- a/tests/test_reservations.py
+++ b/tests/test_reservations.py
@@ -1,7 +1,5 @@
 """Tests for the nwp500.reservations public helpers."""
 
-from __future__ import annotations
-
 from typing import Any
 from unittest.mock import ANY, AsyncMock, MagicMock, patch
 
diff --git a/tests/test_utility_modules.py b/tests/test_utility_modules.py
new file mode 100644
index 00000000..f5e699e5
--- /dev/null
+++ b/tests/test_utility_modules.py
@@ -0,0 +1,149 @@
+"""Tests for previously untested utility modules.
+
+Covers topic_builder, field_factory, and models/_converters.
+"""
+
+import pytest
+from pydantic import BaseModel
+
+from nwp500.field_factory import (
+    energy_field,
+    power_field,
+    signal_strength_field,
+    temperature_field,
+)
+from nwp500.models._converters import (
+    fahrenheit_to_half_celsius,
+    preferred_to_half_celsius,
+    reservation_param_to_preferred,
+)
+from nwp500.topic_builder import MqttTopicBuilder
+from nwp500.unit_system import reset_unit_system, set_unit_system
+
+MAC = "aa:bb:cc:dd:ee:ff"
+
+
+@pytest.fixture(autouse=True)
+def _reset_units():
+    yield
+    reset_unit_system()
+
+
+class TestMqttTopicBuilder:
+    def test_device_topic(self):
+        assert MqttTopicBuilder.device_topic(MAC) == f"navilink-{MAC}"
+
+    def test_command_topic_default_suffix(self):
+        assert (
+            MqttTopicBuilder.command_topic("52", MAC)
+            == f"cmd/52/navilink-{MAC}/ctrl"
+        )
+
+    def test_command_topic_custom_suffix(self):
+        assert (
+            MqttTopicBuilder.command_topic("52", MAC, "ctrl/rsv/rd")
+            == f"cmd/52/navilink-{MAC}/ctrl/rsv/rd"
+        )
+
+    def test_command_topic_wildcard(self):
+        assert (
+            MqttTopicBuilder.command_topic("52", MAC, "#")
+            == f"cmd/52/navilink-{MAC}/#"
+        )
+
+    def test_response_ack_topic(self):
+        assert (
+            MqttTopicBuilder.response_ack_topic("52", MAC, "client-1")
+            == f"cmd/52/navilink-{MAC}/client-1/res"
+        )
+
+    def test_response_topic(self):
+        assert (
+            MqttTopicBuilder.response_topic("52", "client-1", "rsv/rd")
+            == "cmd/52/client-1/res/rsv/rd"
+        )
+
+    def test_event_topic(self):
+        assert (
+            MqttTopicBuilder.event_topic("52", MAC, "st")
+            == f"evt/52/navilink-{MAC}/st"
+        )
+
+
+class TestFieldFactory:
+    def test_temperature_field_metadata(self):
+        class Model(BaseModel):
+            temp: float = temperature_field("DHW temperature", default=0.0)
+
+        extra = Model.model_fields["temp"].json_schema_extra
+        assert extra == {
+            "unit_of_measurement": "°F",
+            "device_class": "temperature",
+            "suggested_display_precision": 1,
+        }
+        assert Model.model_fields["temp"].description == "DHW temperature"
+
+    def test_temperature_field_custom_unit(self):
+        class Model(BaseModel):
+            temp: float = temperature_field("t", unit="°C", default=0.0)
+
+        extra = Model.model_fields["temp"].json_schema_extra
+        assert extra["unit_of_measurement"] == "°C"
+
+    def test_caller_json_schema_extra_merged(self):
+        class Model(BaseModel):
+            temp: float = temperature_field(
+                "t",
+                default=0.0,
+                json_schema_extra={"custom": True, "device_class": "override"},
+            )
+
+        extra = Model.model_fields["temp"].json_schema_extra
+        assert extra["custom"] is True
+        assert extra["device_class"] == "override"  # caller wins
+        assert extra["unit_of_measurement"] == "°F"  # base preserved
+
+    @pytest.mark.parametrize(
+        ("factory", "device_class", "unit"),
+        [
+            (signal_strength_field, "signal_strength", "dBm"),
+            (energy_field, "energy", "kWh"),
+            (power_field, "power", "W"),
+        ],
+    )
+    def test_other_factories_metadata(self, factory, device_class, unit):
+        class Model(BaseModel):
+            value: float = factory("desc", default=0.0)
+
+        extra = Model.model_fields["value"].json_schema_extra
+        assert extra["device_class"] == device_class
+        assert extra["unit_of_measurement"] == unit
+
+
+class TestModelConverters:
+    def test_fahrenheit_to_half_celsius(self):
+        assert fahrenheit_to_half_celsius(140.0) == 120
+
+    def test_preferred_to_half_celsius_us_customary(self):
+        set_unit_system("us_customary")
+        assert preferred_to_half_celsius(140.0) == 120
+
+    def test_preferred_to_half_celsius_metric(self):
+        set_unit_system("metric")
+        assert preferred_to_half_celsius(60.0) == 120
+
+    def test_reservation_param_to_preferred_metric(self):
+        set_unit_system("metric")
+        assert reservation_param_to_preferred(120) == 60.0
+
+    def test_reservation_param_to_preferred_us_customary(self):
+        set_unit_system("us_customary")
+        assert reservation_param_to_preferred(120) == 140.0
+
+    def test_roundtrip_us_customary(self):
+        set_unit_system("us_customary")
+        for temp in (100.0, 120.0, 130.0, 140.0, 150.0):
+            param = preferred_to_half_celsius(temp)
+            assert reservation_param_to_preferred(param) == pytest.approx(
+                temp, abs=1.0
+            )