Unlike the Iris protecting the Stargate on Earth, the shield on the Atlantis Stargate is translucent; the suppressed Unstable vortex and the impact of objects prevented from rematerializing can clearly be seen. The Atlantis shield has yet to be breached by anything because it is placed so close to the event horizon that it blocks even subatomic particles, unlike Earth's iris which can only block objects larger than an atom. However, a "back-door" previously coded into the shield's control system by Dr. Rodney McKay allowed him to remotely deactivate Atlantis' gate shield from an off world location, preventing anyone else (including anyone using the shield's control panel in Atlantis itself) from reactivating it. (SGA: "Rising", "The Return, Part 2")