Press [Tab] during game play to display the
inventory screen. Select the PDA and press E to activate
it. Press G + 0 (zero), then enter one of the following
codes to activate the corresponding cheat function.

Code
Unlimited health 3815
Full health 8745
Medi-Kits has double effect 0132
Double protection 6422
Double damage 7663
All items 7018
All weapons 8700
100% accurate aiming 4394
Enemies are blind 2733
Enemies are deaf 1554
Move silently 0926
Unlimited ammunition 8249