*NOTE: Sentinel Batteries are used to unlock different parts of the Fortress of Doom ship.
Sentinel Crystal
This collectible is obtained on your first visit to the Fortress of Doom during the main story.
Codex: Story of the Sentinels – The Fortress of Doom
You will gain access to the codex after using a Sentinel Battery to unlock a new portion of the ship just after the second mission. The codex will be located in the Slayer’s workshop directly under the bridge.
Praetor Suit Point
This item is obtained as part of the story just after completing the second mission.
Cheat Code
After you use two sentinel batteries to unlock the room containing the original Praetor Suit, head to the hole in the side of the room on the left side. Face the suit and back off the edge, causing you to fall. Be prepared to dash into a secret room below containing the cheat code.
Cheat Code: Fully Upgraded Suit
In the room with the ship’s power source, the cheat code can be found in a duct hanging from the ceiling. Towards the end of the game, one of the windows to the right of the power source will have a red target on it. Shoot this window to turn on a lift pad. Use the lift pad to launch yourself into the duct to collect the cheat code.