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If you have an iPhone, Apple could have your address book, your calendar, your photos, your texts, all the music you listen to, all the places you go—and even how many steps it took to get there, since phones have a little gyroscope in them. Don’t have an iPhone? Then replace “Apple” with Google or Samsung or Verizon. Wear a FuelBand? Nike knows how well you sleep. An Xbox One? Microsoft knows your heart rate.1 A credit card? Buy something at a retailer, and your PII (personally identifiable information) attaches the UPC to your Guest ID in the CRM (customer relations management) software, which then starts working on what you’ll want next.
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Christian Rudder (Dataclysm: Love, Sex, Race, and Identity--What Our Online Lives Tell Us about Our Offline Selves)