In the first film, Professor X mentions to Wolverine that Magneto helped him build it, and therefore knows how to construct helmets with circuitry to block its detection abilities. Cerebro is sabotaged by Mystique so that it injures Professor X, putting him into a coma. The only person seen using Cerebro effectively in the films is Xavier; Jean Grey successfully used the device to locate Magneto in the original film, but the input overwhelmed her nascent telepathic power and left her stunned. This has not been mentioned in the comics, although the Magneto of the comics can use Cerebro, and has designed similar devices.