docs: public void startTracking() {
          if (isTracking) {
              return;
          }
          if (this.session == null) {
              addBroadcastReceiver();
          }        
          // if the session is not null, then add the callback to it right away
          if (getSession() != null) {
              getSession().addCallback(callback);
          }
          isTracking = true;
      }