In the science fiction television show Stargate SG-1, a GDO (" garage door opener ") is a small device carried by SG teams to tell SGC to open the Iris, which protects Stargate Command from invasion through the Stargate itself. Without a GDO, they could not tell if an incoming traveller is friend or foe.
Each SG team and several alien allies are given an IDC to be transmitted with their GDO.
