title: Calculate Distance between Arduino BLE shield and Phone
body: <p>Is it possible to calculate the distance between an arduino bluetooth shield (BLE Shield 2.1) and cell phone?  More specifically, when the cell phone is within &lt;5 feet of the shield, I want it to perform an action.  I know BLE Beacon technology is able to do this in a general sense (immediate, near, far) so I'm wondering if it is possible?</p>
  
  <p>Looking through stack overflow, I've found the following answers but they are all dated:</p>
  
  <p><a href="https://stackoverflow.com/questions/11846506/calculate-distance-between-bluetooth-device-in-android">Answer 1</a> 
  <a href="https://stackoverflow.com/questions/29859666/distance-between-bluetooth-module-and-an-android-device">Answer 2</a></p>
  
  <p>I know that ultrasonic frequency and laser sight are both options but I am trying to keep costs low so I would prefer a way in which the distance is calculated without the use of an additional tool.</p>