diff --git a/homeassistant/components/asuswrt/device_tracker.py b/homeassistant/components/asuswrt/device_tracker.py
index 5d923abf744..fc0a9ee539e 100644
--- a/homeassistant/components/asuswrt/device_tracker.py
+++ b/homeassistant/components/asuswrt/device_tracker.py
@@ -10,6 +10,8 @@ from homeassistant.helpers.entity_platform import AddEntitiesCallback
 from .const import DATA_ASUSWRT, DOMAIN
 from .router import AsusWrtDevInfo, AsusWrtRouter
 
+ATTR_LAST_TIME_REACHABLE = "last_time_reachable"
+
 DEFAULT_DEVICE_NAME = "Unknown device"
 
 
@@ -52,6 +54,8 @@ def add_entities(
 class AsusWrtDevice(ScannerEntity):
     """Representation of a AsusWrt device."""
 
+    _unrecorded_attributes = frozenset({ATTR_LAST_TIME_REACHABLE})
+
     _attr_should_poll = False
 
     def __init__(self, router: AsusWrtRouter, device: AsusWrtDevInfo) -> None:
@@ -97,7 +101,7 @@ class AsusWrtDevice(ScannerEntity):
         self._attr_extra_state_attributes = {}
         if self._device.last_activity:
             self._attr_extra_state_attributes[
-                "last_time_reachable"
+                ATTR_LAST_TIME_REACHABLE
             ] = self._device.last_activity.isoformat(timespec="seconds")
         self.async_write_ha_state()