|“||In an emergency, that shackle is the last line of defense for Warehouse 13!||”|
— Mrs. Frederic, explaining to Artie the purpose of the Shackle, The 40th Floor
The Remati Shackle is a powerful artifact that was designed as a safeguard in case of an attack on Warehouse 13. Since the Sykes assault the shackle has not been seen or mentioned again. By default it might therefore be presumed to still be with Jane Lattimer.
When the Warehouse is attacked, the Shackle creates an impenetrable barrier between the danger and the Warehouse. The barrier also covers the Warehouse's Alternate Entrance which is located several miles from the Warehouse on a mountain. The barrier prevents anything from getting in or getting out, like the cannon ball from Black Bart's Cannon that Marcus Diamond fired at the Warehouse; when the ball exploded against the forcefield, the Shackle absorbed all the energy. The shackle seems to activate automatically as soon as it senses any grave danger to the Warehouse. The barrier will not dissipate until the danger has passed, hinting that it has a degree of prescience. The shackle has to be worn by a person for the barrier to take effect, and the shackle glows blue when the shield activates. When passed on, Adwin Kosan used a key to unlock the shackle and it released a blast of powerful energy.
The only thing that can pass through the shield when it's activated is neutralizer goo, but for some reason even after Artie covered Steve's car with it his car still smashed against the shield.
The Shackle draws its power from the Alpha Centauri star system. After Walter Sykes used the shackle against them by trapping the Regents outside the Warehouse with it, the Regents designed a fail safe so that by redirecting a laser scope at the Innis Observatory, the Shackle won't be drawing its energy from Alpha Centauri, giving the appearance that the shield is still in place while people can still pass right through it. Inanimate objects still won't pass through for some reason.
The only way to remove the shackle is with a special key that Adwin Kosan has around his neck. It appears to cause a minor degree of pain for the wearer immediately upon activation, though this passes soon after.
The Shackle was created by Genghis Khan (to make sure the Mongols kept control of Warehouse 7, as explained by Adwin Kosan). Apparently, Khan went to great and terrible lengths to forge the shackle. It cannot be destroyed by any conventional means. The Regents have developed the tradition, in secret, of passing the Shackle from Regent to Regent, so the Warehouse could be kept safe.
In The 40th Floor, Walter Sykes and his associates executed a plan to destroy the Shackle and weaken the Warehouse; they attempted to destroy the building in Atlanta, Georgia where three Regents (Adwin Kosan, Jane Lattimer and Phillip Petrov) had gathered. The shackle was worn by Phillip, who died during the attack from the corrosion caused by the Berlin Wall Spray Paint, but passed the Shackle onto Jane before he died.
In Stand, Walter Sykes attempted to steal back Carlo Collodi's Bracelet and destroy the Warehouse. While he was in the Ancient Regent Sanctum in Hong Kong, Marcus Diamond fired a cannonball from Black Bart's Cannon which activated the Shackle. The field held up, protecting the Warehouse but trapping everyone inside. It also protected the world from the explosion caused by the House of Commons Masonry that Sykes left behind, containing the blast and only permitting it to destroy the Warehouse.
In Endless Terror, Myka activated the shield's fail safe and redirected its energy flow to Uranus making it so that she, Pete, Artie, and Steve could pass through without any difficulty.