Area 51 Cheats
Cheat: Unlockables
Final Secret:
Get all the secrets to unlock the final secret, which is page 5.
Secret Tapes:
If you scan all five databank items in each stage, you get one secret. Beating
the game yields one secret.
Alien Multi-player Avatar:
If you beat Campaign mode on the Hard difficulty setting, you'll get alien Gray
as a selectable multi-player avatar.
Add cheats for this gameRate these cheats: 
