alarm_pg.pm:
package pg_alarm;

use strict;

sub new {
    shift;
    my $seconds = shift;

    my $self = {};
    $self->{CHILD_PID} = fork();
    if ($self->{CHILD_PID} == 0) {
        sleep($seconds);
    }
    bless $self;
    return $self;
}

sub alarmed {
    my $self = shift;

    my $result = 0;
    if (defined($self->{CHILD_PID})) {
        my $ret = waitpid($self->{CHILD_PID}, 1);
        if ($ret == -1) {
            $result = 1;
        } 
    }
    return $result;
}

1;


test.pl:
use pg_alarm;
use strict;

my $a = pg_alarm->new(10);
while (!$a->alarmed()) {
    #print "haven't gotten alarm yet\n";
}
print "got alarm\n";