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.
cheat function.

Code   Result
-------------
3815 - Unlimited Health 
8745 - Full Health 
0132 - Medi-Kits Double Effect 
6422 - Double Protection 
7663 - Double Damage 
7018 - All Items 
8700 - All Weapons 
8249 - Unlimited 
4394 - 100% Aiming 
6467 - Faster Hacking 
2733 - Enemies are Blind 
1554 - Enemies are Deaf 
0926 - Moving Without Noise