From KOMONews:

Students at the University of Washington volunteered their phones to see how easy it can be to see where the device has been. The frequent locations setting creates a map, and tapping on a specific locations reveals the dates and times of a particular visit and even how long you were there.

The students were taken aback that it was so easy to track their history.

“That’s kind of crazy,” Sebastian Aste said. “It’s interesting how accessible your life can be.”