Docs update

Author: nseidle

docs/firmware_update_um980.md

@@ -18,7 +18,7 @@ The UM980 is the GNSS receiver inside the RTK Torch. The following describes how
 
     *Startup message showing passthrough mode*
 
-    **Note:** The RTK device will stay in this passthrough mode until the external power button is pressed and released.
+    **Note:** The RTK device will stay in this passthrough mode until the external power button is pressed and released. The device will beep when exiting passthrough mode.
 
     ![Connect button and connection settings in UPrecise](<img/UPrecise/SparkFun RTK Everywhere - UPrecise Inteface Connect.png>)