Regent Street in London has debuted a smartphone app that is linked with beacon technology. So far, 130 stores, or roughly 80% of the retailers along Regent Street’s mile-long strip, have installed sensors at their entrances that can communicate directly with nearby phones and other mobile devices carrying the app. Mark Scott explains that the effort is part of a long-running, $1.6 billion improvement program for the shopping street, which is 200 years old and owned almost entirely by the Crown Estate, the British government’s property management organization.