[ALUG] How to check if a cron.daily job has run?

I run a daily backup on four systems. It's a bash script called 'backup' (original eh?) which is in /etc/cron.daily and thus gets run by Anacron in the early morning. I need to check that the backup has run somehow as, very occasionally, the backup system's USB disk 'falls asleep' and as a result any attempt to access it just hangs. Thus the rsync backup job doesn't fail (and produce an error message) it just never returns. So how can I check and get an error message if this happens? The next day is soon enough, it's not an urgent problem, I just need to know if my daily backups are working. However this needs to be 'no message means it has worked', message only if it has not worked. -- Chris Green