Personal cloaking device
From The Stargate Omnipedia
Wearable technology that makes the user invisible to the naked eye. It is particularly favored by the former Goa'uld System Lord Nirrti. The user of this technology can be made visible with a T.E.R.
KEY EPISODES
Out of Mind - Hathor uses a personal cloaking device to hide from SG-1 when she captures them and recreates the S.G.C.
Fair Game - The System Lords learn that Nirrti possesses cloaking technology.
Rite of Passage - Nirrti returns using her cloak in attempt to remain undetected as she studies Cassandra's illness.
Metamorphosis - Nirrti uses her cloak to protect herself from Samantha Carter.