The government contends that Carpenter lacks a constitutionally protected privacy interest in his location data because his cellphone was continually sharing that data with his cellphone provider. Privacy advocates are rightly alarmed by this argument. Much of the digital technology all of us rely on today requires us to share information passively with third parties. Visiting a website, sending an email, buying a book online – all of these things require sharing sensitive data with internet service providers, merchants, banks and others. If this kind of commonplace and unavoidable information-sharing is sufficient to extinguish constitutional privacy rights, the digital-age fourth...