Pass Card

In Fallout 3, pass cards are items that are randomly encountered. The cards serve no other purpose than causing the protectrons to help you fight nearby enemies when in the associated subway lines. (Red, Blue)

Locations
Pass cards are located in random places throughout the Capital Wasteland. They are dropped by ghouls, centaurs, and may also be found on trogs if The Pitt is installed.

A ghoul has 1.5% chance of dropping a pass card of either color. A centaur has a chance of 0.6% and trogs have an even smaller chance of about 0.4%.