sterretje:
The Southco EA-A06-001 uses USB. So you need a USB host shield.I did a quick search but could not (quickly) find a link where people succeeded in using serial communication though an USB host shield; not said it can't be done.
Are you prepared to modify the Southco EA-A06-001? If so, open it up and take sharp photos and post here.
Assuming I have a USB shield, how can I make the arduino send the command to the Lock Controller?
Which pin in the arduino can i use to send a string command to the lock controller?
and no I would prefer not to modify the lock controller.