Prey contains so many hidden secrets. In the Trauma Center, you can find a hidden safe that doesn't require a code.
Enter Mathias Kohl's office, which is found along the left-hand side of the Trauma Center right after Hendrick DeVries' office. Go to the computer at the back and click "begin behavioral test." This will bring up on the other computer in this office the same test Morgan Yu goes through at the beginning of the game.
Go to this other computer and answer the questions in this order: A, C, B, A, C. After answering the last question in that sequence, the painting on the direct opposite wall as the computer will lift up revealing a safe with a Transcribe and 3 Neuromods.