Mark state final in BinarySensorEntity (#51234)

homeassistant/components/binary_sensor/__init__.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 
 from datetime import timedelta
 import logging
+from typing import final
 
 import voluptuous as vol
 
@@ -150,12 +151,14 @@ class BinarySensorEntity(Entity):
     """Represent a binary sensor."""
 
     _attr_is_on: bool | None = None
+    _attr_state: None = None
 
     @property
     def is_on(self) -> bool | None:
         """Return true if the binary sensor is on."""
         return self._attr_is_on
 
+    @final
     @property
     def state(self) -> StateType:
         """Return the state of the binary sensor."""