Constrictor Harness

"The Constrictor Harness will compress your torso upon activation, allowing you to enter narrow spaces. Using the Constrictor Harness prevents you from breathing properly. Prolonged use will cause damage eventually death due to lack of oxygen."

―In-game description.

B.J. uses the constrictor harness to squeeze through narrow space.

The Constrictor Harness allows B.J. to access certain openings and passages which are otherwise too small to fit through, allowing the player to move quickly and quietly through an area using routes which enemies cannot enter or see into or hide underneath certain objects. Its associated battery of secondary abilities primarily benefit a "Stealth" playstyle.

Abilities

• Kobra: The Constrictor Harness' main function, allowing entrance into small places while crouched. Activated by crouch-walking into appropriate apertures while aiming at them. Staying in these cramped spaces too long causes health to start to deplete slowly, but most such areas are quick enough to navigate that this isn't an issue unless one stays concealed inside them for an extended period of time.
• Silent Step: Normal movement is made completely silent just like crouch-walking, and sprinting is significantly quieter. This makes stealth play significantly less tedious as the player can move faster through certain areas without increasing their risk of being detected.
• Terror-Billy: Enemies will freeze in terror upon seeing B.J., which is represented in-game as a brief period of slow motion. Getting behind cover immediately when this triggers can sometimes cancel the enemy's awareness but it's generally more effective to use the window to bring a silenced weapon to bear or close the distance for a melee takedown without other enemies being alerted. Enemies can still bring their weapons to bear whiled slowed down and if they manage to fire a shot the alarm will be raised as usual. This ability works against all human enemies (soldiers, Commanders, Übercommanders and Klansmen) and Supersoldaten but not against Kampfhunde or robots.
• Iron Lung: an upgrade to the basic Kobra ability which increases the time that the constrictor harness can be used for before health starts to deplete. Unlocked by completing Habib Ismail's side quest on the Eva's Hammer.

Location

If not selected as the initial contraption, the Constrictor Harness can be found in the Nuclear Bunker during the relevant Übercommander mission.