Google ($GOOG) is developing a wearable medical device consisting of a magnet that would collect ingested nanoparticles whose job it is to attach to cancerous cells and take them to the magnet. The nanoparticles convey data to the magnet by "lighting up" cancer cells, Andrew Conrad, the head of Google's life sciences unit, said. The development-stage device, worn around the wrist, is being tested on mock arms. For the "lighting up" of cancerous cells to be detected, Conrad needed to study how light travels through skin. "When they were casting and making these arms they had to make them out of materials that behaved like skin," Conrad said. Watch The Atlantic's video