Survive Sevastopol with Prima’s Alien: Isolation Walkthrough.
As the third mission begins, your objective will be to Find an Elevator to Seegson Communications. Step off the transit car and explore the area you're in. You can go to the right, but your objective will be found up the stairs to the left. We found several locked doors but weren't able to enter, so we continued looking around until we passed through the only door we could and our objective updated.
The game will now ask you to Take the Elevator Up to Seegson Communications, and when you climb the stairs, a woman will begin shooting at you. Briefly duck, but when she runs off, feel free to explore the entire up and downstairs, minus the exact door the woman was standing at. Scavenge for supplies, and when you're ready, go to the door that is opposite of the one you entered this area through. This will trigger a cut scene where you pick up the Access Tuner, and soon after the woman will return with three angry friends.
Your new objective will be to Find a Data Cell to Repair the Security Access Tuner, but you have four hostile people approaching from the top floor, just to the right of where you originally entered this area. Turn around from where you picked up the Access Tuner and head up the stairs to your right, then move around the balcony in a counterclockwise fashion. You will now be able to go through a door that was previously locked. In fact, it's the same door the four humans just entered the area through. Congratulations, you just gave them the slip.
If the four bad people spotted you, they will talk as if they are going to chase you down the stairs, but will quickly decide against that idea. Head down two flights of stairs and grab the map, then go down one more level and through the door with the Tech Support sign above it. There will be a vent on your left that you can snag some supplies from, but your ultimate destination is the office a bit further ahead.
Go up the stairs toward the office, stopping to grab the map before you head inside. With map in hand, go into the office and save your game, then pick up the Revolver and Keycard laying on the desk. Turn around from where you picked up those two items and go down the short hallway, using the Keycard to pass through the door.
Loot this entire room, making sure to go down the hall with the System Monitoring sign above it and searching the dead body and room at the far end. Make sure to snag the Flashbang blueprints off the wall near the body full of bullet holes, then backtrack down the hall to return to the main room, turning left and heading through the door with the Sevastopol Works Archive sign above it.
Entering the room will trigger a cut scene, and when it ends there will be an alarm going off. That's the bad news. The good news is that we can help you deal with this unfortunate situation, and that starts with you turning to your right and pressing the big button on the device with the hand crank on it. In fact, you're going to press the button on two of those devices, moving from your left to right. When you move the second device you'll expose the Data Cell. Approach and pick it up to update your objective, which is now to Hack the Elevator to Seegson Communications.
It's time to head back out the door that you used to enter this area, but to do so you'll have to use your Access Tuner. Approach the door and follow the on-screen prompts to tune into the code system and then to enter the code shown. Doing this successfully will open the door and return you to the large room. Head back into the hallway with the System Monitoring sign above it, but this time use your Access Tuner to unlock the side room. Head inside and pick up any goodies laying around, including the audio log laying on the desk.
Exit the room and go all the way back through the office where you collected the Revolver and Keycard, then go down the stairs next to the office and into the hallway with the Tech Workshop sign above it. It's about this time that your objective will update to Disable Security Lockdown, so approach the Tech Workshop door and use your Access Tuner to get inside.
Enter the room and use the Sevastolink terminal in the corner, then when you're done, spend a moment going through the entire room. Whatever you do, don't interact with the keyboard that gives you the option to Disable Security Lockdown just yet. It might be harmless, but we took one more safety precaution before doing so.
On the opposite side of the same wall that you entered the Tech Workshop, there will be a door where you can use your Maintenance Jack. It doesn't seem overly important since it only leads back to the same hallway you were in before, but let's just say it's never a bad idea to have multiple escape routes. We're not giving anything away... we genuinely don't know if this is necessary. We're just the careful type.
With your alternate escape route ready to go, head back to the desk in the middle of the room and press the button to Disable Security Lockdown. This will trigger a cut scene, and when it's over, it's time to get a move on before the Alien shows up and does all those horrible things that were shown in videos prior to the game's launch.
It's time to head all the way back to the room where you gave the slip to those four angry humans. We're pretty sure you're safe(ish), but sneaking won't hurt, so slowly work your way back up and use your Access Tuner to unlock the door. When you go through, hide behind the railing and observe the Alien at work.
Once the Alien scurries away, work your way down the stairs and to the elevator where you originally picked up the Access Tuner. Use it to open the door, then get inside and press the button on the wall to bring this mission to a close.
Continue to Alien: Isolation - Mission 4: Seegson Communications.