Keypads are button based mechanisms in both System Shock and System Shock 2 that regulate entry through the doors that they control. They need the code to open them or they can be hacked (in System Shock 2).
System Shock[]
They are encountered by the Hacker on the Citadel Station on Levels R-6.
System Shock 2[]
They are encountered by soldier on Earth and the Von Braun (except Hydroponics) and are manufactured by TetraCorp.
System Shock (Remake)[]
They are encountered by the Hacker on the Citadel Station