To adjust the volume:
* 3 0 # <Master PIN> # <3 to increase volume/6 to decrease volume> #
During the volume setting, you may press 3 or 6 repeatedly to get your desired volume, before exiting the menu with '#' on the keypad.
To mute, decrease the volume to minimum. Keypad will blink on mute to indicate key press.
Note: If the volume does not change further then that is the maximum or minimum. There are 5 volume levels, excluding the muted volume.