scanbd is available in the repositories and with some system changes can recognize when a scanner button is pushed and take some action.
https://wiki.archlinux.org/index.php/Scanner_Button_Daemon
http://virantha.com/2014/03/17/one-touch-scanning-with-fujitsu-scansnap-in-linux/
http://superuser.com/questions/1043092/sane-scanning-scanbd-buttons-and-service-permissions
https://github.com/mdengler/scanbd/blob/master/doc/README.txt