use strict;
use Tk;
use Tk::StayOnTop;
use Win32::OLE qw(in);


# Seriennummer ermitteln:
my $computer = Win32::NodeName();
my $WMI = Win32::OLE->GetObject("WinMgmts://$computer");
my @results = in($WMI->ExecQuery("select SerialNumber from Win32_BIOS"));
my $serialnumber = $results[0]->{SerialNumber};


# Fenster erzeugen
my $myWindow = MainWindow -> new(
        -title => "Serial Number",
);
$myWindow -> resizable ('0','0');                    # Größe nicht änderbar
my $screenHeight = $myWindow->screenheight;          # ernittle Bildschirmhöhe
my $screenWidth   = $myWindow->screenwidth;          # ernittle Bildschirmbreite
$myWindow->geometry($screenWidth."x".$screenHeight); # Fenster maximieren
$myWindow->overrideredirect(1);                      # Rahmen entfernen
$myWindow->StayOnTop;
...