[tiwil]

This really helps, but I think after their 7 days free trial you need to subscribe for a plan.

Hmmmmm.. I don't really understand. The web write you've 7 days free trial and no credit card required. But on the pricing, you can get $0/months.

Btw, I also suggest you to use UptimeRobot as you can use custom domain to check it, and can monitor up to 50 things at the same time. But, it's checking every 5 minutes.

Btw, good tutorial, I hope you can clear our ambiguity.