Set Netgear device entities to unavailable when the device is not con…

…nected (#135362)

homeassistant/components/netgear/router.py

@@ -210,6 +210,12 @@ async def async_update_device_trackers(self, now=None) -> bool:
 
         for device in self.devices.values():
             device["active"] = now - device["last_seen"] <= self._consider_home
+            if not device["active"]:
+                device["link_rate"] = None
+                device["signal"] = None
+                device["ip"] = None
+                device["ssid"] = None
+                device["conn_ap_mac"] = None
 
         if new_device:
             _LOGGER.debug("Netgear tracker: new device found")

homeassistant/components/netgear/sensor.py

@@ -344,6 +344,11 @@ def __init__(
         self._attr_unique_id = f"{self._mac}-{attribute}"
         self._state = device.get(attribute)
 
+    @property
+    def available(self) -> bool:
+        """Return if entity is available."""
+        return super().available and self._device.get(self._attribute) is not None
+
     @property
     def native_value(self):
         """Return the state of the sensor."""