how to get into security room?

[Moederjager]

I want to unlock new charachters i am playing with an friend and i just cant find the code to the room

[ODS_Jungsoo]

Hi! For now you need to play single mode you unlock new characters! Also, you do not need a code to get into unlock them.

If you are referring to a room you see when you first enter the game which requires a code - that is a bonus room and you can find a code while playing the game which you can check in your inventory!

[Yuki]

The code to the security room is something different. Im not sure if its the same for everyone but...

You loot the code. To me at least its 4413E2. Every time. The first time i had to take a look into my inventory to get it, every further run its already put in just greyed out, so you can just enter it without looking it up. The room as one loot container and one starting buff, usually of high quality.

The code wont get you new agents though. Those come from:

Those random door rooms. Level 2 has one in the lobby, its where i found Mr. Boyscout.
Level 3 had a room with Beaker- in the same run actually!
And Scalpel was Level 4, but several runs later.
Its random what you get. You will know before opening the room because you can "hear" (read) them through the door.

The Boyscout/Beaker run was after i purchased the game, not sure if its part of the demo. It wasnt the first run with the Full Version though, there is some randomness.
Oh and you dont switch within the run, they will then become available in your command center.