Cerebro is a device used by Charles Xavier to enhance his telepathy for the purposes of long-range detection of mutants. The device is located in the sub-basement of Xavier's, in a large open structure.
Cerebro amplifies the brainwaves of the user. In the case of telepaths, it can detect traces of other mutants worldwide. Not much has been shown about how powerful it is; it has been shown to have a trans-continental range for detecting mutants, but during the Great Mutant Headache, mutants and humans across the globe were affected by it. Cerebro is specifically tooled for Xavier's brain patterns, meaning only he has full access to all the abilities, but all psis can use at least some level of the machine, dependent on their power levels and their familiarity with Cerebro itself.
Cerebro works by specifically using the telepathic user's brain patterns as a template for a long-range scan, detecting the subtle differences in brain chemistry between mutants and humans. To detect the presence of a mutant is no easy task, the more minds in an area, the more difficult to pinpoint a single one. The attempt has been compared to finding one red raindrop in the middle of a downpour. Once a mutant is located, however, a skilled user can attempt to discern more about the mutant, although this takes intense concentration and years of training and experience with Cerebro. To date, only Professor Xavier and Jean Grey have successfully used Cerebro to scan for mutants.
It is theorized that there may be a temporary link between a telepath's mind and the structure of the machine when Cerebro is in use. This is due to the unique mental processes of telepaths, but is also a serious risk should Cerebro be sabotaged or break down during use. At one point, Cerebro was tampered with by Mystique, with the resulting feedback sending Professor Xavier into a short coma.
The Cerebro unit is built into a large chamber beneath the mansion, resembling the interior of a hollow sphere. The panels on the wall act as amplifiers and buffers for psionic energy, to the point where people in the chamber who are not using Cerebro may see visual images of what the user is currently sensing with the device. There is a small control unit on a platform extending over the center of the chamber, but the main interface with Cerebro is a helmet worn by the user, allowing direct mental interface with the machine.
While initially designed by Charles Xavier and Magneto, Xavier has modified the design over time to be both more powerful and more resistant to tampering after both the sabotage by Mystique and the co-opting of the designs by William Stryker.
A replica of Cerebro was built at Stryker's Alkali Lake compound, and was intended to use Xavier's power to kill all mutants on the planet. This attempt failed, however, and both the replica Cerebro and all the information on it were destroyed when the Alkali Lake Dam burst and flooded the compound.
In January 2015, the Dark Phoenix destroyed the mansion and co-opted Cerebro, using Sarah Vale's powers to forge a deeper connection in an attempt to use the lives of all high-level mutants to increase her own abilities. She was stopped by Jean Grey with both being killed in the battle, but not before 80% of the world's mutants spontaneously combusted.
In March 2015, Charles announced that Cerebro was being dismantled. His public reason, for the "frankenberry world" residents, was that Cerebro had been damaged by the psychic backlash of M-Day. The true reason, revealed in an email to the various team members who had come from the 'old' universe, was that he could no longer justify keeping Cerebro, when it was repeatedly used for genocide. The burden of guilt from the deaths of hundreds of thousands of mutants was too much for Charles to bear, and he destroyed not only the machine, but all plans and research relating to it. The area that once housed Cerebro has not been repurposed, although it is still locked off for now.