I know there are webservices dedicated for knock, but I like the idea behind this app, it allows check simply the status code, or run a custom JavaScript on the sites you choose.
Nock Nock is a simple app which allows you to monitor your websites for maximum uptime.
The app will automatically knock on the door of your websites (or web servers) on a chosen interval to make sure they are up and responding successfully. If something is wrong, you get a notification telling you so.
The F-Droid version is a beta, and is more updated than the release you will find on the Github page:
Nock Nock is a simple app which allows you to monitor your websites for maximum uptime.
The app will automatically knock on the door of your websites (or web servers) on a chosen interval to make sure they are up and responding successfully. If something is wrong, you get a notification telling you so.

The F-Droid version is a beta, and is more updated than the release you will find on the Github page: