Mimic devices are alien technology from P3X-118. An individual is passed through a large scanning device which uploads his exact image into a small round holographic sequencer, or mimic device. When the device is placed anywhere on the body and activated, one can instantly take on the appearance of the person scanned. The aliens of P3X-118 used the mimic devices in conjunction with a second device, worn at the temple, which accessed the thoughts of the scanned individual, and they were able to impersonate and replace SGC personnel and establish a foothold situation, or alien incursion, of the base.
Following the foothold incident, the scanning device and 12 of the mimic devices were recovered, including those programmed to duplicate O'Neill, Daniel, Fraiser, and Major Davis, and they were taken to Area 51 for study. Although the alien devices created holographic images that seemed to last indefinitely, those that were reverse engineered by scientists in the lab were only sustainable for three to four minutes at a time due to problems with electromagnetic interference.
After months of research with limited success, the program was shut down. Dr. Langham, one of the scientists assigned to the research project, stole the 12 mimic devices and replaced them with fakes, then staged his own disappearance and provided the devices to the Committee, a shadow organization working in cooperation with rogue NID agents. By order of the Committee, the devices were used by rogue NID agent Mark Devlin to frame O'Neill for the attempted assassination of Senator Kinsey. The devices were recovered when the assassination plot was averted by Carter and Agent Barrett's investigation. The device used by Carter to impersonate Devlin while reporting to the Committee sustained an image for six and a half minutes, a new record.