title: Calculate approximated distance using RSSI
body: <p>I working on a project that aims to measure approximated distance between single Raspberry PI and nearby smartphone.</p>
  
  <p>The final target of the project is to check if there is a smartphone in the same room of the Raspberry.</p>
  
  <p>I thought on two ways for implementation. The first is measure distance using RSSI value, second is to calibrate the setup in the first time from many places in the room and outside the room and get a threshold RSSI value.
  I read that smartphones sends wi-fi packets even when the wi-fi is disabled, I thought to use this feature the get the RSSI value from the transmitting smartphone (Using kismet passively) and check if its in the room. I can use Bluetooth RSSI also.</p>
  
  <p>How can I calculate distance using RSSI?</p>