Cheat mode
At the main menu, press Up(2), Down(2), Circle, Down, Up, Circle to unlock the "Cheat" option at the title screen. Select the "Cheat" option, then enter one of the following case-sensitive codes to activate the corresponding cheat function, which can be toggled on or off (except for "All levels and emergencies"):

All levels and emergencies
Enter "KEYTOTHECITY" as a code to unlock all levels and emergencies.

Long range stungun
Enter "FRYINGTIME" as a code.

Minigun instead of pistol
Enter "MINIFUN" as a code.

Mk. 3 assault rifle with unlimited grenades
Enter "ULTIMATEPOWER" as a code.

Mk. 4 pistol
Enter "ZEROTOLERANCE" as a code.

Bullets set fire to enemies
Enter "BURNINGBULLET" as a code.

Thermal breather Mk. 2 has better smoke visibility
Enter "ISEEYOU" as a code.

Disco mode
Enter "DANCINGFEET" as a code.

Terror mode
Enter "BURNERSREVENGE" as a code.

Squeaky voices
Enter "WHATWASTHAT" as a code.

No heads
Enter "KEEPYOURHEAD" as a code.