Unofficially, a "Garage Door Opener." The device transmits an encoded signal from an off-world team through the Stargate's wormhole
to be received by the S.G.C. computer
, identifying the SG unit or ally. Upon signal confirmation base personnel will then open the iris covering the Stargate, allowing the inbound traveler(s) to enter the base safely.
A G.D.O. and iris code (a sequence of numbers that must be manually entered into the G.D.O.) is assigned to every member of every SG team, and to a small number of alien allies including the Tok'ra and Jaffa Master Bra'tac. The codes can be altered if one of the devices is compromised.
Serpent's Song - The Tok'ra are issued their own G.D.O. and iris code.
Unnatural Selection - Probing O'Neill's mind, the advanced Replicators uncover his G.D.O. code.