diff --git a/homeassistant/components/saunum/__init__.py b/homeassistant/components/saunum/__init__.py
index 32ccc7bd6e2e58..b014abfeb2c0ba 100644
--- a/homeassistant/components/saunum/__init__.py
+++ b/homeassistant/components/saunum/__init__.py
@@ -14,6 +14,7 @@
 PLATFORMS: list[Platform] = [
     Platform.CLIMATE,
     Platform.LIGHT,
+    Platform.SENSOR,
 ]
 
 type LeilSaunaConfigEntry = ConfigEntry[LeilSaunaCoordinator]
diff --git a/homeassistant/components/saunum/icons.json b/homeassistant/components/saunum/icons.json
new file mode 100644
index 00000000000000..854fcee7ff55d1
--- /dev/null
+++ b/homeassistant/components/saunum/icons.json
@@ -0,0 +1,9 @@
+{
+  "entity": {
+    "sensor": {
+      "heater_elements_active": {
+        "default": "mdi:radiator"
+      }
+    }
+  }
+}
diff --git a/homeassistant/components/saunum/quality_scale.yaml b/homeassistant/components/saunum/quality_scale.yaml
index af6674e6d6ddf1..ef3ea07669b182 100644
--- a/homeassistant/components/saunum/quality_scale.yaml
+++ b/homeassistant/components/saunum/quality_scale.yaml
@@ -60,10 +60,10 @@ rules:
     comment: Integration controls a single device; no dynamic device discovery needed.
   entity-category: done
   entity-device-class: done
-  entity-disabled-by-default: todo
+  entity-disabled-by-default: done
   entity-translations: done
   exception-translations: done
-  icon-translations: todo
+  icon-translations: done
   reconfiguration-flow: done
   repair-issues:
     status: exempt
@@ -74,5 +74,7 @@ rules:
 
   # Platinum
   async-dependency: todo
-  inject-websession: todo
+  inject-websession:
+    status: exempt
+    comment: Integration uses Modbus TCP protocol and does not make HTTP requests.
   strict-typing: todo
diff --git a/homeassistant/components/saunum/sensor.py b/homeassistant/components/saunum/sensor.py
new file mode 100644
index 00000000000000..7e9a09e051783d
--- /dev/null
+++ b/homeassistant/components/saunum/sensor.py
@@ -0,0 +1,99 @@
+"""Sensor platform for Saunum Leil Sauna Control Unit integration."""
+
+from __future__ import annotations
+
+from collections.abc import Callable
+from dataclasses import dataclass
+from typing import TYPE_CHECKING
+
+from pysaunum import SaunumData
+
+from homeassistant.components.sensor import (
+    SensorDeviceClass,
+    SensorEntity,
+    SensorEntityDescription,
+    SensorStateClass,
+)
+from homeassistant.const import EntityCategory, UnitOfTemperature, UnitOfTime
+from homeassistant.core import HomeAssistant
+from homeassistant.helpers.entity_platform import AddConfigEntryEntitiesCallback
+
+from . import LeilSaunaConfigEntry
+from .entity import LeilSaunaEntity
+
+if TYPE_CHECKING:
+    from .coordinator import LeilSaunaCoordinator
+
+PARALLEL_UPDATES = 0
+
+
+@dataclass(frozen=True, kw_only=True)
+class LeilSaunaSensorEntityDescription(SensorEntityDescription):
+    """Describes Leil Sauna sensor entity."""
+
+    value_fn: Callable[[SaunumData], float | int | None]
+
+
+SENSORS: tuple[LeilSaunaSensorEntityDescription, ...] = (
+    LeilSaunaSensorEntityDescription(
+        key="current_temperature",
+        translation_key="current_temperature",
+        native_unit_of_measurement=UnitOfTemperature.CELSIUS,
+        device_class=SensorDeviceClass.TEMPERATURE,
+        state_class=SensorStateClass.MEASUREMENT,
+        value_fn=lambda data: data.current_temperature,
+    ),
+    LeilSaunaSensorEntityDescription(
+        key="heater_elements_active",
+        translation_key="heater_elements_active",
+        state_class=SensorStateClass.MEASUREMENT,
+        value_fn=lambda data: data.heater_elements_active,
+    ),
+    LeilSaunaSensorEntityDescription(
+        key="on_time",
+        translation_key="on_time",
+        native_unit_of_measurement=UnitOfTime.SECONDS,
+        suggested_unit_of_measurement=UnitOfTime.HOURS,
+        device_class=SensorDeviceClass.DURATION,
+        entity_category=EntityCategory.DIAGNOSTIC,
+        entity_registry_enabled_default=False,
+        state_class=SensorStateClass.TOTAL_INCREASING,
+        value_fn=lambda data: data.on_time,
+    ),
+)
+
+
+async def async_setup_entry(
+    hass: HomeAssistant,
+    entry: LeilSaunaConfigEntry,
+    async_add_entities: AddConfigEntryEntitiesCallback,
+) -> None:
+    """Set up Saunum Leil Sauna sensors from a config entry."""
+    coordinator = entry.runtime_data
+
+    async_add_entities(
+        LeilSaunaSensorEntity(coordinator, description)
+        for description in SENSORS
+        if description.value_fn(coordinator.data) is not None
+    )
+
+
+class LeilSaunaSensorEntity(LeilSaunaEntity, SensorEntity):
+    """Representation of a Saunum Leil Sauna sensor."""
+
+    entity_description: LeilSaunaSensorEntityDescription
+
+    def __init__(
+        self,
+        coordinator: LeilSaunaCoordinator,
+        description: LeilSaunaSensorEntityDescription,
+    ) -> None:
+        """Initialize the sensor."""
+        super().__init__(coordinator)
+        self._attr_unique_id = f"{coordinator.config_entry.entry_id}-{description.key}"
+        self.entity_description = description
+
+    @property
+    def native_value(self) -> float | int | None:
+        """Return the value reported by the sensor."""
+        return self.entity_description.value_fn(self.coordinator.data)
diff --git a/homeassistant/components/saunum/strings.json b/homeassistant/components/saunum/strings.json
index 8b986423bc577d..003d48fb734c2d 100644
--- a/homeassistant/components/saunum/strings.json
+++ b/homeassistant/components/saunum/strings.json
@@ -34,6 +34,15 @@
       "light": {
         "name": "[%key:component::light::title%]"
       }
+    },
+    "sensor": {
+      "heater_elements_active": {
+        "name": "Heater elements active",
+        "unit_of_measurement": "heater elements"
+      },
+      "on_time": {
+        "name": "Total time turned on"
+      }
     }
   },
   "exceptions": {
diff --git a/tests/components/saunum/snapshots/test_sensor.ambr b/tests/components/saunum/snapshots/test_sensor.ambr
new file mode 100644
index 00000000000000..ae5c73d07b5423
--- /dev/null
+++ b/tests/components/saunum/snapshots/test_sensor.ambr
@@ -0,0 +1,168 @@
+# serializer version: 1
+# name: test_entities[sensor.saunum_leil_heater_elements_active-entry]
+  EntityRegistryEntrySnapshot({
+    'aliases': set({
+    }),
+    'area_id': None,
+    'capabilities': dict({
+      'state_class': <SensorStateClass.MEASUREMENT: 'measurement'>,
+    }),
+    'config_entry_id': <ANY>,
+    'config_subentry_id': <ANY>,
+    'device_class': None,
+    'device_id': <ANY>,
+    'disabled_by': None,
+    'domain': 'sensor',
+    'entity_category': None,
+    'entity_id': 'sensor.saunum_leil_heater_elements_active',
+    'has_entity_name': True,
+    'hidden_by': None,
+    'icon': None,
+    'id': <ANY>,
+    'labels': set({
+    }),
+    'name': None,
+    'options': dict({
+    }),
+    'original_device_class': None,
+    'original_icon': None,
+    'original_name': 'Heater elements active',
+    'platform': 'saunum',
+    'previous_unique_id': None,
+    'suggested_object_id': None,
+    'supported_features': 0,
+    'translation_key': 'heater_elements_active',
+    'unique_id': '01K98T2T85R5GN0ZHYV25VFMMA-heater_elements_active',
+    'unit_of_measurement': 'heater elements',
+  })
+# ---
+# name: test_entities[sensor.saunum_leil_heater_elements_active-state]
+  StateSnapshot({
+    'attributes': ReadOnlyDict({
+      'friendly_name': 'Saunum Leil Heater elements active',
+      'state_class': <SensorStateClass.MEASUREMENT: 'measurement'>,
+      'unit_of_measurement': 'heater elements',
+    }),
+    'context': <ANY>,
+    'entity_id': 'sensor.saunum_leil_heater_elements_active',
+    'last_changed': <ANY>,
+    'last_reported': <ANY>,
+    'last_updated': <ANY>,
+    'state': '0',
+  })
+# ---
+# name: test_entities[sensor.saunum_leil_temperature-entry]
+  EntityRegistryEntrySnapshot({
+    'aliases': set({
+    }),
+    'area_id': None,
+    'capabilities': dict({
+      'state_class': <SensorStateClass.MEASUREMENT: 'measurement'>,
+    }),
+    'config_entry_id': <ANY>,
+    'config_subentry_id': <ANY>,
+    'device_class': None,
+    'device_id': <ANY>,
+    'disabled_by': None,
+    'domain': 'sensor',
+    'entity_category': None,
+    'entity_id': 'sensor.saunum_leil_temperature',
+    'has_entity_name': True,
+    'hidden_by': None,
+    'icon': None,
+    'id': <ANY>,
+    'labels': set({
+    }),
+    'name': None,
+    'options': dict({
+      'sensor': dict({
+        'suggested_display_precision': 1,
+      }),
+    }),
+    'original_device_class': <SensorDeviceClass.TEMPERATURE: 'temperature'>,
+    'original_icon': None,
+    'original_name': 'Temperature',
+    'platform': 'saunum',
+    'previous_unique_id': None,
+    'suggested_object_id': None,
+    'supported_features': 0,
+    'translation_key': 'current_temperature',
+    'unique_id': '01K98T2T85R5GN0ZHYV25VFMMA-current_temperature',
+    'unit_of_measurement': <UnitOfTemperature.CELSIUS: '°C'>,
+  })
+# ---
+# name: test_entities[sensor.saunum_leil_temperature-state]
+  StateSnapshot({
+    'attributes': ReadOnlyDict({
+      'device_class': 'temperature',
+      'friendly_name': 'Saunum Leil Temperature',
+      'state_class': <SensorStateClass.MEASUREMENT: 'measurement'>,
+      'unit_of_measurement': <UnitOfTemperature.CELSIUS: '°C'>,
+    }),
+    'context': <ANY>,
+    'entity_id': 'sensor.saunum_leil_temperature',
+    'last_changed': <ANY>,
+    'last_reported': <ANY>,
+    'last_updated': <ANY>,
+    'state': '75.0',
+  })
+# ---
+# name: test_entities[sensor.saunum_leil_total_time_turned_on-entry]
+  EntityRegistryEntrySnapshot({
+    'aliases': set({
+    }),
+    'area_id': None,
+    'capabilities': dict({
+      'state_class': <SensorStateClass.TOTAL_INCREASING: 'total_increasing'>,
+    }),
+    'config_entry_id': <ANY>,
+    'config_subentry_id': <ANY>,
+    'device_class': None,
+    'device_id': <ANY>,
+    'disabled_by': None,
+    'domain': 'sensor',
+    'entity_category': <EntityCategory.DIAGNOSTIC: 'diagnostic'>,
+    'entity_id': 'sensor.saunum_leil_total_time_turned_on',
+    'has_entity_name': True,
+    'hidden_by': None,
+    'icon': None,
+    'id': <ANY>,
+    'labels': set({
+    }),
+    'name': None,
+    'options': dict({
+      'sensor': dict({
+        'suggested_display_precision': 2,
+      }),
+      'sensor.private': dict({
+        'suggested_unit_of_measurement': <UnitOfTime.HOURS: 'h'>,
+      }),
+    }),
+    'original_device_class': <SensorDeviceClass.DURATION: 'duration'>,
+    'original_icon': None,
+    'original_name': 'Total time turned on',
+    'platform': 'saunum',
+    'previous_unique_id': None,
+    'suggested_object_id': None,
+    'supported_features': 0,
+    'translation_key': 'on_time',
+    'unique_id': '01K98T2T85R5GN0ZHYV25VFMMA-on_time',
+    'unit_of_measurement': <UnitOfTime.HOURS: 'h'>,
+  })
+# ---
+# name: test_entities[sensor.saunum_leil_total_time_turned_on-state]
+  StateSnapshot({
+    'attributes': ReadOnlyDict({
+      'device_class': 'duration',
+      'friendly_name': 'Saunum Leil Total time turned on',
+      'state_class': <SensorStateClass.TOTAL_INCREASING: 'total_increasing'>,
+      'unit_of_measurement': <UnitOfTime.HOURS: 'h'>,
+    }),
+    'context': <ANY>,
+    'entity_id': 'sensor.saunum_leil_total_time_turned_on',
+    'last_changed': <ANY>,
+    'last_reported': <ANY>,
+    'last_updated': <ANY>,
+    'state': '1.0',
+  })
+# ---
diff --git a/tests/components/saunum/test_sensor.py b/tests/components/saunum/test_sensor.py
new file mode 100644
index 00000000000000..9fa223ecaa010f
--- /dev/null
+++ b/tests/components/saunum/test_sensor.py
@@ -0,0 +1,85 @@
+"""Test the Saunum sensor platform."""
+
+from __future__ import annotations
+
+from dataclasses import replace
+
+from freezegun.api import FrozenDateTimeFactory
+from pysaunum import SaunumException
+import pytest
+from syrupy.assertion import SnapshotAssertion
+
+from homeassistant.const import STATE_UNAVAILABLE, Platform
+from homeassistant.core import HomeAssistant
+from homeassistant.helpers import entity_registry as er
+
+from tests.common import MockConfigEntry, async_fire_time_changed, snapshot_platform
+
+
+@pytest.fixture
+def platforms() -> list[Platform]:
+    """Fixture to specify platforms to test."""
+    return [Platform.SENSOR]
+
+
+@pytest.mark.usefixtures("entity_registry_enabled_by_default", "init_integration")
+async def test_entities(
+    hass: HomeAssistant,
+    snapshot: SnapshotAssertion,
+    mock_config_entry: MockConfigEntry,
+    entity_registry: er.EntityRegistry,
+) -> None:
+    """Test all entities."""
+    await snapshot_platform(hass, entity_registry, snapshot, mock_config_entry.entry_id)
+
+
+async def test_sensor_not_created_when_value_is_none(
+    hass: HomeAssistant,
+    mock_config_entry: MockConfigEntry,
+    mock_saunum_client,
+) -> None:
+    """Test sensors are not created when initial value is None."""
+    base_data = mock_saunum_client.async_get_data.return_value
+    mock_saunum_client.async_get_data.return_value = replace(
+        base_data,
+        current_temperature=None,
+        heater_elements_active=None,
+        on_time=None,
+    )
+
+    mock_config_entry.add_to_hass(hass)
+
+    assert await hass.config_entries.async_setup(mock_config_entry.entry_id)
+    await hass.async_block_till_done()
+
+    assert hass.states.get("sensor.saunum_leil_temperature") is None
+    assert hass.states.get("sensor.saunum_leil_heater_elements_active") is None
+    assert hass.states.get("sensor.saunum_leil_on_time") is None
+
+
+@pytest.mark.usefixtures("init_integration")
+async def test_entity_unavailable_on_update_failure(
+    hass: HomeAssistant,
+    mock_saunum_client,
+    freezer: FrozenDateTimeFactory,
+) -> None:
+    """Test that entity becomes unavailable when coordinator update fails."""
+    entity_id = "sensor.saunum_leil_temperature"
+
+    # Verify entity is initially available
+    state = hass.states.get(entity_id)
+    assert state is not None
+    assert state.state != STATE_UNAVAILABLE
+
+    # Make the next update fail
+    mock_saunum_client.async_get_data.side_effect = SaunumException("Read error")
+
+    # Move time forward to trigger a coordinator update (60 seconds)
+    freezer.tick(60)
+    async_fire_time_changed(hass)
+    await hass.async_block_till_done()
+
+    # Entity should now be unavailable
+    state = hass.states.get(entity_id)
+    assert state is not None
+    assert state.state == STATE_UNAVAILABLE