There are other ways you could use Monit to keep an eye on your MySQL replication processes, but this one is simple and involves no external dependencies:
check file mysql-slave with path /var/lib/mysql/master.info
if timestamp > 5 minutes then alert
If the slave process stops, then the master.info file doesn't get updated with changing binlog positions and Monit will send an alert. Obviously this depends on MySQL's implementation, and isn't as decoupled as a 'SHOW SLAVE STATUS' solution, but it's a lot simpler.
MySQL seems to update the binlog every few minutes if the slave is running. If you need quicker alerts, this method isn't for you!
