I know that there are a lot of them (more than 170).
Let's miss the part of the point of building yet another one, since I've already launched it and now, apart from fixing bugs I'm looking for unique selling proposition.
Maybe you use pingdom, uptimerobot and others, and you're not satisfied?
I wrote an article about something more-or-less unique https://victor-ponamariov.medium.com/a-way-of-detecting-if-your-site-was-hacked-1e7ad06ae4ab, but still not sure if it worth implementing it.
Another thing is "Transactional checks", when you can tell service that it should:
- visit your page
- submit a form
- see something as result
Similar to functional testing, like you have a set of actions.
This thing looks very promising thought Pingdom has it.
Something my uptime monitoring service doesn't have: they inspect SSL certificates for expiry, but don't inspect the full trust chain. The certificate of the SSL provider (who signed our key) got replaced. With more abstraction (resellers) we got no notification. Until it expired, making our SSL certificate invalid, too. That caused avoidable downtime.