Start a new game on The Old House level. In the kitchen area, there's an intercom on the right hand side, by the door. Keep checking it, for it will start blinking. When it does so, click on it with the mouse cursor to hear a distorted voice say something along the lines of: "3:30. Balcony. Input. Year of Mandela's Death."
Once you've heard the message(which should unlock the achievement "The message"), survive until 3:30. At that time, go to the Balcony, and enter a report for Balcony/Outside with the anomaly type "Input". (This anomaly type choice only becomes available at 3:30, if you've listened to the message.) Send it.
A green text input box will appear in the bottom middle portion of the screen. Click on it and write "2013", then press enter. The screen will turn black, and the achievement unlocks. (And you get to watch a secret "ending"!)