use strict;
use warnings;

BEGIN {
   package Testing;
   use Tie::Scalar qw( );
   BEGIN { our @ISA = qw(Tie::StdScalar); }
   sub STORE {
      my ($self, $val) = @_;
      print("STORE ", defined($val) ? "[$val]" : 'undef', "\n");
      shift->SUPER::STORE(@_)
   }
}

{
   our $s;
   tie $s, 'Testing';
   {
      print("pre\n");
      local $s;
      print("post\n");
   }
   print("\n");
   {
      print("pre\n");
      local $s = 'a';
      print("post\n");
   }
}

##</code><code>##

pre
STORE undef   # local
post
STORE undef   # local unroll

pre
STORE undef   # local
STORE [a]     # assignment
post
STORE undef   # local unroll

##</code><code>##

use Sub::ScopeFinalizer qw( scope_finalizer );

sub local_sassign {
   my $r = \($_[0]);
   my $sentry = scope_finalizer { $$r = $_[0] } { args => [ $$r ] };
   $$r = $_[1];
   return $sentry;
}

sub f {
   my $sentry = local_sassign $SIG{ALRM}, \&alarm_handler;
   ...
}