These monitoring services are very easy to implement yourself. Create a console app and with like two lines of code do a Get on a url using .NET's WebClient class.  Windows scheduler can execute the app once every x minutes. You can do this on your home computer and you can ping your public sites as often as you want and you don't have to pay anyone for a similar service. 

The app can be more advanced where it can log into a site which needs user authentication. Or create the app as a Windows service. Years ago I created such an app where if any of my sites are not responding, the app would call or text my phone.