Question

Is there any way to read rssi value from 3 modem at the same time in android without connecting any of them

Answer 1

In conjunction with the previous answer, you can add code inside of the following timer to check it every few seconds. Of course you can modify how long you want the timer to execute.

 var timer = new Timer();
         timer.Tick += new EventHandler(timer_Tick);
         timer.Interval = 2000; //2 seconds
         timer.Start(); 

 void timer_Tick(object sender, EventArgs e)
{
    ..your code here..
}