A Reflex Shield is a modified version of the Imperium's void shield technology used by the Raven Guard to hide their ships from the enemy. Essentially a void shield in reverse, a reflex shield is calibrated to a higher tolerance and redirected inwards so that all matter and energy generated by the ship is displaced into the Warp. This effectively makes Raven Guard ships with active reflex shields immune to all forms of detection, as even visible light reflected off ship's hull is displaced, and due to low power requirements the reflex shields can be maintained indefinitely. When activated a Raven Guard ship will appear to shimmer briefly before going completely invisible to both the naked eye and scanners.
One serious downside to the use of reflex shields is that they significantly reduce a ship's sensor capabilities, essentially making them half-blind. Unlike traditional void shields they also provide no protection against attacks, and it can take several minutes for the void shield generators to switch between the two modes. In addition reflex shields have a relatively low energy threshold above which they will no longer work. At most a ship's reactors can only run at half-power and still remain invisible.