A couple of weeks ago I wanted to setup one of my machines that runs Kubuntu 15.04 to lock the computer when the smartcard is removed from the reader. After reading through a few other articles on this, I came up with the following solution.

The first thing that I learn't was that scdaemon is able to notify other applications about reader status change events, and this is done by placing an executable script called scd-event in ~/.gnupg.

Basic steps:

1. Create ~/.gnupg/scd-event
2. Make sure to make the script executable: chmod +x ~/.gnupg/scd-event
3. Use the script below as a template - adapt it to do what you.

#!/bin/sh
PGM=scd-event

reader_port=
old_code=0x0000
new_code=0x0000
status=

tick='`'
prev=
while [ $# -gt 0 ]; do
  arg="$1"
  case $arg in
      -*=*) optarg=$(echo "X$arg" | sed -e '1s/^X//' -e 's/[-_a-zA-Z0-9]*=//')
            ;;
         *) optarg=
            ;;
  esac
  if [ -n "$prev" ]; then
    eval "$prev=\$arg"
    prev=
    shift
    continue
  fi
  case $arg in
      --help|-h)
          cat <<EOF
Usage: $PGM [options]
$PGM is called by scdaemon on card reader status changes

Options:
  --reader-port N        Reports change for port N
  --old-code 0xNNNN      Previous status code
  --old-code 0xNNNN      Current status code
  --status USABLE|ACTIVE|PRESENT|NOCARD 
                         Human readable status code

Environment:

GNUPGHOME=DIR            Set to the active homedir

EOF
          exit 0
          ;;
    
      --reader-port)  
          prev=reader_port
          ;;
      --reader-port=*)
          reader_port="$optarg"
          ;;
      --old-code)  
          prev=old_code
          ;;
      --old-code=*)
          old_code="$optarg"
          ;;
      --new-code)  
          prev=new_code
          ;;
      --new-code=*)
          new_code="$optarg"
          ;;
      --status)  
          prev=status
          ;;
      --new-code=*)
          status="$optarg"
          ;;

      -*)
          echo "$PGM: invalid option $tick$arg'" >&2
          exit 1
          ;;

      *)
          break
          ;;
  esac
  shift
done
if [ -n "$prev" ]; then
  echo "$PGM: argument missing for option $tick$prev'" >&2
  exit 1
fi

cat <<EOF
========================
port:     $reader_port
old-code: $old_code
new-code: $new_code
status:   $status
EOF

if [ x$status = xNOCARD -a x$prev != xNOCARD ]; then
    # In KDE5 the following line will invoke the screensaver lock
    qdbus org.freedesktop.ScreenSaver /ScreenSaver Lock
fi