The vo'carr was a rare piece of Goa'uld technology which was similar in design to the vo'cume, and like the vo'cume it projected a holographic recording which had been programmed into it by a powerful Goa'uld. Unlike the vo'cume, which was designed to instruct Jaffa warriors in the name of their god, the vo'carr was meant to be a historical device which detailed the triumph of a powerful System Lord. The device had no external buttons, but was activated by simply pressing a section on the top.
Only two such devices are known of by the Tau'ri, one chronicling Apophis' defeat of a rival System Lord, which was seen by Teal'c while he was still in Apophis' service, and another which chronicled the defeat and exile of Phobos by Ares. SG-1 discovered the latter of the devices on a planet which was guarded by Apophis' Serpent Guard and learned of Phobos' fate, and at the same time discovering the Stargate address to Kar'tek, which they would soon visit. (SG1: "Fall of Rome Prequel")