There are several people not having a key to the "MaschinenRaum" and they don't wanna get out of bed just for standing in front of a locked door. So we decided to let the door tweet whether it's locked or not.
We started with a LPT cable that is connected to the parallel port on our server. On the other end there is a switch inside the door that is pressed by the bolt as soon as the door is locked. When the button is pressed, pin 10 of the LPT cable which usually carries 4.5V is grounded. We can now monitor this state of change with a tool called "pin" provided by the "parashell" package and send out a tweet with the help of a cron job and "blt".