title: Prove that 2 mobile devices are close to each other
body: <p>Let's say I'm developing an app (Android, iOS or both), and 2 users (UserX &amp; UserY) have downloaded my app with giving it all permissions needed,</p>
  <p>If UserX opened the app telling it &quot;hey app, I'm currently close to UserY's mobile&quot; (like in the same room or something), where UserY's mobile could be just laying down doing nothing,</p>
  <p><strong>Question is</strong>, can the app make sure UserX's claims are valid or not? .. if yes, then is it valid for both platforms (Android &amp; iOS)?</p>