I've this code ... stripped a bit
Qt Code: 
  1. void testform::keyPressEvent(QKeyEvent *event)
  2. {
  3.     switch (event->key())
  4.     {
  5.         case Qt::Key_4 :
  6.             if (!demo_started)
  7.             {
  8.                 this->buttons[0]->setPixmap(QPixmap::fromImage(images[1]));
  9.                 this->listener = new PortListener(portName);
  10.  
  11.                 // So, connect to listener, and ... all happy :P
  12.                 connect(this->listener,SIGNAL(packet_received(data_answer)),
  13.                         this,SLOT(packet_received(data_answer)));
  14.  
  15.             }
  16.             else
  17.             {
  18.                 this->buttons[0]->setPixmap(QPixmap::fromImage(images[0]));
  19.                 this->killTimer(demo_timer_id)
  20.             }
  21.             demo_started = !demo_started;
  22.             break;
  23.    ...................................
  24.         default : QWidget::keyPressEvent(event);
  25.     }
  26. }
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and receiver SLOT:
Qt Code: 
  1. void testform::packet_received(data_answer answer)
  2. {
  3.     qDebug() << "pewpew all dead !";
  4.     redrawUI();
  5. }
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Problem is that this slot called only when I move mouse,press key etc. But signal itself emmited every 0.5 seconds (read data from com-port). Listener class is quite stable and works as intended.