TcpClient MyTcpClient;
int myPort = 4000;
StreamWriter MyWriter;
StreamReader MyReader;

int port = GetFreePort();

MyTcpClient = new TcpClient(IPAddress.Loopback.Tostring(), port);
MyTcpClient.ReceiveTimeout = 30000;

MyReader = new StreamReader(MyTcpClient.GetStream());
MyWriter = new StreamWriter(MyTcpClient.GetStream());

while(MyTcpClient.Connected) //if device is off, it still true
{
    string line = MyReader.ReadLine();// when device is off, it is null
}