Area 51 Cheats

Rebel Kronn warrior:
Shoot the first three S.T.A.A.R. team members and nothing else at the beginning of the game. After the first human is shot, you will not be harmed by any gun fire. After the third human is shot, you will transform into an alien in the main hallway of the first level. You will have infravision when playing as an alien, which allows targets to be more visible.

Secret rooms:
Enable the "Secret rooms" option. Do any one of the following to enter a room called Chow Palace, which is filled with power-ups.

Inside the bunker, shoot all the blue lights on the left wall.
Shoot out all the back windows inside the bunker.
When riding inside the forklift, shoot all the yellow barrels.
When riding inside the jeep, shoot all the yellow boxes.
When you are in the building shoot the name plate off the second door as it is opening.
When you are being bombarded by the two aliens on top of the hill, shoot everything yellow.