The Sodan cloak, an example of Ancient technology, creates a shield of invisibility. Used by the Sodan warriors of P9G-844, the device consists of a leather armband worn on the arm with a triangular blue crystal that activates the cloak when pressed. Instantly, the individual wearing the armband fades to invisibility. The Sodan used the device to shield themselves from their enemies and to protect their sacred grounds. When Volnek was overcome by the curse of the Prior and his madness drove him to kill his own people, he also used the cloak to attack unseen.
The Sodan cloaking device emits an energy field around the wearer that puts him slightly out of phase with our normal dimension of space-time. Whoever is in the dimensional field is essentially accessing a pocket of subspace, making him virtually undetectable. Although the cloak is based on phase-shift technology, however, it has several distinguishing characteristics that set it apart from similar technology of Ancient design such as Merlin's phase-shift device. Typically, an individual that has been shifted out of phase cannot physically interact with those in a different phase, however the Sodan cloak enables a warrior to remain invisible and still fire his weapon at his uncloaked enemies in another phase. The devices appear to access the same spatial dimension, and cloaked warriors appear visible to each other, however they do not access exactly the same dimension as Merlin's phase-shift device. When Mitchell had been shifted out of phase by Merlin's device, and Teal'c had used the Sodan cloak to become invisible, they were able to see, hear, and communicate with each other while out of phase, but could not physically interact.
Following the slaughter of the Sodan, the cloaking devices were brought back to Earth and stored at the SGC and Area 51. They were tested for safety, and it was discovered that the devices emit a significant amount of radiation. The SGC assumed that the radiation was a coincidental byproduct of the technology, and although the Sodan would have been protected from such radioactivity by their symbiotes, the SGC made modifications to the technology to shield the radioactive emissions in order to make the devices safer for human use. Several SG teams began employing the cloaking devices for off-world missions that required inconspicuous covert observation, and one device stolen from Area 51 by members of the Trust was used covertly on Earth, however soon afterward horrific monstrous creatures began appearing on the worlds where the modified cloaking devices had been used. Through testing, it was determined that parasitic leech-like creatures from an alternate dimension were randomly bleeding through and crossing into our dimension when caught within the dimensional field of the modified cloaking device. The radioactive output of the original design had performed a vital function by repelling the inter-dimensional parasites, but the SGC's modification and shielding of that radiation had allowed the parasites to cross into our phase. The parasites had then entered indigenous animals, causing the transformation into dangerous predatory monsters.
The SGC immediately discontinued the use of the Sodan cloaking devices, however they have been used sparingly since then, carefully taking into account safe levels for radiation exposure. When Carter was shifted out of phase by Merlin's phase-shift device and then unexpectedly drawn into an alternate reality, the team used the Sodan cloak, hoping to be able to see and communicate with her while she was out of phase. When Vala allowed her memory to be altered as part of a plan to lure Adria to another world for capture, she had also taken one of the devices with her, and lost it in a game of chance.
Cross Reference: Alternate Dimension, Ancients, Area 51, Inter-Dimensional Parasites, Invisibility, Merlin's Phase-Shift Device, Sodan, Trust, Volnek
Episode Reference: Babylon, The Fourth Horseman, Arthur's Mantle, Uninvited, Dominion