Dead Ringers

From the Introduction: No one knew that ghosts fed off wireless communications. Ghosts are hungry for information. For years, they have been reading our emails and looking at our photos posted on social networking sites. They've seen the videos of ourselves and our cats and they've heard our mobile phone calls. And now they want to replace us. Those who have been replaced are virtually indistinguishable from the original, and any casual acquaintance wouldn't know the difference.