We can test the default audio input device, or the only audio input device on a simplistic configuration
arecord -vvv -f dat /dev/null
Watch while the audio input levels are displayed as a percentage.
We can specify an audio input device
arecord -vvv --device="hw:1,0" -f dat /dev/null
You can display a list of CAPTURE Hardware Devices. To figure out what audio input device is at hw: card,device use the following command
arecord -l
The output look for "Card X" and on the same line "device X" to know the card,device combination to specify.