class x :public QObject
{
   Q_OBJECT
private:
   x(){ qApp()->installEventFilter(this); }
   static x* theInstance;
public:
   x* getInstance()
   {
      if(theInstance == NULL)
      {
         theInstance = new x;
      }
      return x;
   }
   virtual bool eventFilter ( QObject * watched, QEvent * event )
   {
      if (event->type() == QEvent::KeyPress) 
      {
         emit signalKeyPress((QKeyEvent *)event);
      }
      return false;
   }
signals:
   signalKeyPress(QKeyEvent *);
};

x* x:theInstance  = NULL;

connect(x::getInstance(), SIGNAL(signalKeyPress(QKeyEvent *)), 
             someObject, SLOT(slotKeyPress(QKeyEvent *))));