Back in the original Subnautica, there was a doomsday artifact inside of the weapon emplacement that was unusable. However, it seems to have shown back up in Below Zero!
To start, you have to enable the developer console. Press f3 to open the menu, then press f8 to enable clicking on the menu. Change the option named "Disable console" to be unchecked, and press ~ on most computers to open the console.
Getting the Item
Warning: Do not do this on a survival world that you intend to play legitimately, as there is almost no way to undo this command.
Open the console and type in:
- unlock all
This will unlock every blueprint, except for a few not meant to be accessed. Next, type in:
This will allow you to craft any item without needing resources. This step is optional, although makes it much easier.
Go to the fabricator, go to the Personal section, and then the Equipment section.
On the second-to-last row, you should see a few items. If you are unfamiliar with what the Doomsday device looked like, you can also just hover the mouse cursor over each item until you find the one named "Biosample Placeholder"
Proceed to craft the item.
Placing the Item in a Base
This bit is the most complicated, but easy once you get the hang of it. Since items cannot be dropped while in a base, you have to cheese it.
Create an empty Large Room, and then attach a Large Room Partition to one of the walls. It must not be attached to anything else for this to work. Once it is placed, leave your base through a hatch, then swim back to roughly where the partition was inside the base.
Swim into the specific bit of the wall the partition connected to, and you should swim straight through. Once inside the base, you can freely now drop the artifact and swim back to a hatch and re-enter the base normally.
However, be warned that the partition glitch works both ways, as you can fall through it while inside your base and take fall damage.
In addition, the artifact likes to move around. Very slowly, but it'll move. I personally boxed mine in with partitions, but feel free to do whatever you feel is best! This will be patched in a later version, but for now, enjoy!