Ask HN: How do you get notifications if something doesn't happen?

I have searched high and low for a service and I could have sworn I saw a solution on HN but I cannot find it.

In particular I am looking for a solution that can notify me if my hourly backups were NOT completed.

What I have come up with is a script that checks the modified timestamp of my backup file and then checks if it is older than 1 hour. If it is, then the script returns 200 success headers. If it doesn't then it returns a 404.

I am then monitoring that page with an uptime monitoring service.

I'm curious what everyone else does and how well it works for you.