Code 3
From The Stargate Omnipedia
S.G.C. alert, typically used when there is an infiltrator already inside the base, such as a Goa'uld. Zat'ni'katels and T.E.R.'s are made readily available during a Code 3.
KEY EPISODE
Rite of Passage - Cassandra tells Carter and Dr. Fraiser that she sensed the presence of a Goa'uld.