The Pip-Boy 3000 Mark IV is a pre-War Personal Information Processor (PIP) in Fallout 4 manufactured by RobCo Industries and acts as a database for the wearer's personal information and inventory. It is an updated version of the Pip-Boy 3000.
The Pip-Boy 3000 Mark IV is a multi-functional device that features a built-in Geiger counter and has been programmed to display the wearer's stats, area maps, inventory, and item properties. Its screen also acts as a flashlight in low visibility areas and it has a dial for tuning into radio frequencies. It is a more ergonomically designed and up-to-date version of the Pip-Boy 3000 used in other vaults and according to its start-up screen.
A unique feature of the Pip-Boy 3000 Mark IV is an adapter plug attached to the underside of the device. This plug is used to perform diagnostics on power armor, as well as open and close the main doors of vaults in the Commonwealth, effectively making the Pip-Boy a vault key.