An iris is a device designed to prevent unwanted incomming gate traffic developed by Stargate Command. The iris is a metallic barrier several millimeters from the event horison of an active stargate. Anything that goes through a stargate with a closed iris at the destination will fail to rematerialize and be destroyed. Radio waves can pass through a gate, allowing SG teams to send confirmation codes to get through using a specialized transmitter known as a GDO (Garage Door Opener). For security reasons, each Stargate Team is issued a specific GDO code for each time they use the Stargate.