Hannah Fry delves into the inner workings of virtual assistants, such as Google Assistant and Siri, which are now found in almost half of all UK homes.

Hannah goes behind the scenes with Alexa's chief scientist, reveals how secret technology invented to hunt U-boats led to their targeted hearing, and discovers modern wireless networks' debt to a 1940s Hollywood star.

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.