In addition to BrowserUK's suggestion of $|++; # Disable buffering on STDOUT. , the order of the mode change seems significant.

This works:

use Win32::Console ;

$cons = new Win32::Console(STD_INPUT_HANDLE) || die "Can't open new co
+nsole\n";
$|++; # Disable buffering on STDOUT.


ConsoleMode_AND_WITH (~(ENABLE_ECHO_INPUT));# 
ConsoleMode_AND_WITH ( ~(ENABLE_LINE_INPUT));#   
 
while (1) {
    $char = $cons->InputChar(1) ;
    last if ord $char == 13 ;
    print '*' ;
    $password .= $char ;
}
print "\nPassword was $password\n" ;
$cons->Mode($oldMode) ;

sub ConsoleMode_AND_WITH(){
  my $o = $cons->Mode();
  $cons->Mode($o & shift);  
  print "--Mode change from $o\[" . unpack(q(H2),chr($o)) . " ]  to  "
     . $cons->Mode() . "[". unpack(q(H2),chr($cons->Mode())) . "]\n";
}
[download]

Changing the order of ConsoleMode_AND_WITH calls produces the "Requires ENTER key" behaviour before anything shows up.

MS documentation says ENABLE_LINE_INPUT OFF should ignore the setting of ENABLE_ECHO_INPUT. But this is probably getting off-topic. Anyway, the code above does what you require, as does Browser's.