0451 was a code first used to unlock a vault in the game Deus Ex, published by Eidos Montreal. Since then, this code has showed up multiple times in a number of video games, including Deus Ex: Human Revolution. It is a reference to the book Fahrenheit 451. The code for the first door in System Shock was 451, a System Shock 2 door had 45100 as a code, and Bioshock had a room that required the code 0451 to enter. This number is now recognized by many Deus Ex fans. The art director of Eidos Montreal even tweeted to his followers that one of his flight numbers was 0451, and stated that Deus Ex fans would know what that meant.
Ammunition is disappearing again, so we're changing the door code for the comm van near the helipad. New Code: 0451.