We recently updated our website and all the monitoring we created on UptimeRobot worked on the new site without any additional configuration.

I like that it offers a free way to check that your website is up from outside of my network and whitelisted IP addresses. Once setup, I don't have to do anything and it will notify me if and when it goes down. Then again once it's up. This way I don't freak out if I see the email late and didn't catch it on when it went down. The free plan does pretty much everything a single website owner could ask for. If you have many sites to check then you'll have to upgrade but I found it cheaper than most of the other solutions available.

It is a good value in comparison with some more advanced tools that include similar features. It also is fairly easy to get the hang of and seutp.