The following are known Action Replay Codes for Spy Hunter on Nintendo Game Boy Advance (GBA).
These codes were also known as GameShark Codes and in most cases will work on both devices.

These codes are for the U.S. version of the game.

Master Code – Must Be On
2dc9f80d
32c1f055
eefd7bd4
abecb2bf

All Missions Open
ba20843f
5071f7fd

Invisible
4b3603c2
9b5a5a00

Infinite Turbo
5f273dc2
47f50397

Infinite Guns
d666ee77
c67dc92a

Infinite Rockets
3a3d2b95
ead00f3f

Infinite Time
cae7caca
7d5fefa2

Infinite Oil
dc92739b
8208609a