gistfile1.pl

use IO::Async::Timer::Periodic;
use strict;
use warnings;
use IO::Async::Loop;
use LWP::UserAgent;
use HTTP::Request::Common qw(HEAD);
my $ua   = LWP::UserAgent->new;
my $loop = IO::Async::Loop->new();

my $code = 0;

my $timer = IO::Async::Timer::Periodic->new(
    interval       => 10,
    first_interval => 0,
    on_tick        => sub {
        my $res = $ua->request( HEAD "http://store.apple.com" );
        return if($res->code, $code);
        $code = $res->code;
        if($code == 404) {
            `say "Apple Store is down!"`;
        } else {
            `say "Apple Store back up!"`;
        }
    },
);

$timer->start;
$loop->add($timer);
$loop->loop_forever;

See my AnyEvent-based version of this script at https://gist.github.com/1094704