This shows you how to see the live volume of sound devices on Linux. I've tested this on Raspbian Jessie.
pulseaudio -D
pactl list source short
pavumeter alsa_input.usb-0d8c_C-Media_USB_Headphone_Set-00-Set.analog-mono ** Message: Starting in playback mode. ** Message: Using device 'alsa_input.usb-0d8c_C-Media_USB_Headphone_Set-00-Set.analog-mono'