The Secret Genius of Modern Life: Season 1, Episode 5

1 - 5: Fitness Tracker

With around a third of the population now owning fitness trackers, Britain has become a nation obsessed with tracking its every move.

Hannah Fry finds out how 1970s car crashes helped us to count our steps, why high-altitude WWII dog-fights led to a crucial health monitor and how fitness trackers are even being used to catch killers.