Citizen Sleeper Steam Key Game Activation: 1. Open Steam 2. Click on the Games menu 3. Select "Activate a Product on Steam" 4. Enter the serial key and click Continue, then follow the on-screen instructions (Please enter the code manually or via copy-paste). After that, the game will automatically be added to your library and can be downloaded immediately. Once the download is complete, the game will be ready to play. The game will be available in your Library.