code to for global hot keys

keycapture.vala

void main(string[] args) {
	Gtk.init (ref args);
	Gdk.Window win = Gdk.get_default_root_window ();

	win.add_filter(null, filter_func);
	
	unowned X.Display display = Gdk.X11.get_default_xdisplay ();
	display.grab_key (display.keysym_to_keycode('C'),
					  Gdk.ModifierType.CONTROL_MASK | Gdk.ModifierType.SHIFT_MASK,
					  Gdk.X11.get_default_root_xwindow(),
					  false, X.GrabMode.Async, X.GrabMode.Async);
					  
	Gtk.main ();
}

Gdk.FilterReturn filter_func(Gdk.XEvent gdk_xevent, Gdk.Event ev) {
	Gdk.FilterReturn filter_return = Gdk.FilterReturn.CONTINUE;


	X.Event *xevent = (X.Event *) gdk_xevent;
	if (xevent->type == X.EventType.KeyPress) {
		stdout.printf ("Keycode: %u\n",xevent->xkey.keycode);
	}

	return filter_return;
}