title: Alert when two users/friends are near to each other - Android Proximity
body: <p>I tried searching but i couldn't find anything.
  My Question is "<strong>How can i alert 2 or more users if they are nearby each other?</strong>" in android using Geo-fencing or something else.</p>
  
  <p>Say, If a UserA is in football ground and UserB walking nearby that football ground. Then UserA and UserB automatically gets notification that UserA/UserB are somewhere nearby.</p>