During your stay on Talos I you will come across a number of different locked doors and safes that need to be opened. Most of the time these areas contain valuable materials, treasure, and items that you can use in crafting. One of the first safes you encounter early on is in the Security Office on the bottom floor of the Talos I lobby. To get into this room you will need to obtain the keycard via the I.T. room on the second floor. A more detailed explanation of this task is here, but once you have it make your way back downstairs.
Just be cautious when you go into the I.T. room because two Phantoms will be waiting for you. Unlock the Security Office and head to your right where the small office is with the shotgun on the desk. Pick up the shotgun, ammo, and any other items that are laying around this.
Skim through the emails on the computer and then turn around to face the safe against the wall directly behind you. Input the code 0526 to unlock the safe and grab the contents inside of it. In this safe, there are a few shotgun shells, a Recycler Charge, an EMP Charge, and and the very powerful Nullwave Transmitter. Try to save this item for when you come face to face with the more dangerous version of Phantoms as it will cancel out their abilities to teleport, rendering them helpless to your bullets. After all, you are going to need all the help you can get in Prey.