For six weird weeks in the fall of 2004, Udo Wächter had an unerring sense of direction. Every morning after he got out of the shower, Wächter, a sysadmin at the University of Osnabrück in Germany, put on a wide beige belt lined with 13 vibrating pads — the same weight-and-gear modules that make a cell phone judder. On the outside of the belt were a power supply and a sensor that detected Earth’s magnetic field. Whichever buzzer was pointing north would go off. Constantly.