diff --git a/include/android/sensor.h b/include/android/sensor.h
index 6112d5f..eef69f4 100644
--- a/include/android/sensor.h
+++ b/include/android/sensor.h
@@ -267,7 +267,8 @@
      * {@link ASENSOR_TYPE_HEAD_TRACKER}
      * reporting-mode: continuous
      *
-     * Measures the orientation and rotational velocity of a user's head.
+     * Measures the orientation and rotational velocity of a user's head. Only for internal use
+     * within the Android system.
      */
     ASENSOR_TYPE_HEAD_TRACKER = 37,
     /**