While exploring the Talos I station in Prey, you can find locked safes. Opening them requires you to know a four-digit keycode. Below, you can find the solution of the puzzle connected to the first safe you come across after exiting the apartment in which experiments were conducted on Yu. When you're in Simulation Labs of the Neuromod Division, you have to go to the Simulation Debriefing.
Once there, carefully examine the whiteboard shown in the picture. It contains the partially blurred keycode.
The valid keycode for the safe is 5150. Approach the safe shown in the above image and enter the code. The safe contains PSI PSI Hypo Plan and the [O] PsiV-AMP .24 Scope Chipset.