The keypad is a pad used for opening a room full of Meca-Penguins in the Teleportation Center.
The keypad is given to Twinsen by Lanktir the first time he speaks with him, saying that it has been mailed to him by mistake. Twinsen can use it in a door in the Teleportation center to enter a room full of Meca-Penguins, but it isn't very usefull, as he can only carry one at a time.
Inventory Description[]
"Keypad that controls a digital locking system. Once placed on one door inside the Teleportation Center, it allows access to a room full of Meca-Penguins."