Instead of setting $SIG{ALRM} :
    local $SIG{ALRM} = sub { die "alarm" };

try something like the following:
    use POSIX qw(SIGALRM);
    POSIX::sigaction(SIGALRM,
        POSIX::SigAction->new(sub { die "alarm" }))
          or die "Error setting SIGALRM handler: $!\n";