It basically pings your site every 5 minutes and checks for an html status code of 200 OK. If it gets anything different or can't make a connection it should send you an email. I need to add some logging so people can view it's history. I'm also going to add element checking, so that for any given URL, you can add something on the page that you want it to check too, like whether or not a link exists or a button, etc.
It would be worth spending 10 minutes to write up some quick copy to that effect. When I entered my URL, I felt like it went into a black hole as there was no mention of "what happens now".