Foxtrot Alpha Six
From The Stargate Omnipedia
Military alert code issued at the start of the Foxtrot Alpha Six simulation, warning Stargate Command personnel that an intruder has breached the iris and invaded the complex.
Because the training simulation is based around the threat, this alert code likely exists at the real Stargate Command.
KEY EPISODE
Avatar - Sergeant Harriman issues the Foxtrot Alpha Six alert at the beginning of each round of the virtual reality unit simulation.