Cerebra amplifies the brainwaves of the user. In the case of telepaths, it can detect traces of other mutants worldwide. It is not clear whether it finds mutants by the power signature they send out when they use their powers or by the presence of the X-gene in their body; both methods have been used. Anyone other than a highly powerful or trained telepath who uses this machine would fall into a "psychic coma" because of the overwhelming brain signatures of people around the area they searched. Only powerful telepaths with significant experience and control can effectively use it. Replacing Cerebro, Cerebra is a machine the size of a small room in the basement of Xavier's School for Higher Learning. It resembles a pod filled with a sparkling fog that condenses into representations of mental images.
