diff --git a/How-to-upgrade-4G-extension-firmware.md b/How-to-upgrade-4G-extension-firmware.md
index c0d4a43..6bf7d30 100644
--- a/How-to-upgrade-4G-extension-firmware.md
+++ b/How-to-upgrade-4G-extension-firmware.md
@@ -196,6 +196,14 @@ https://techship.com/faq/how-to-automated-connection-establishment-with-sim7600-
 
 # Useful AT commands
 
+* check firmware version
+```
+echo -en "AT+GMR\r\n" | sudo socat - /dev/ttyUSB2,crnl
++GMR: LE20B04SIM7600G22
+OK
+
+```
+
 * check sim card status
 ```
 echo -en  "AT+cpin?\r\n" |sudo socat - /dev/ttyUSB2,crnl