Detect from browser if specific application is installed

We have an advanced webpage (ASP.NET, C#), and a application which needs to be installed on the client computer in order to utilize the webpage to its fullest. The application is a tray app, and has primarily two tasks. Detect when certain events happen on the webserver (for instance invited to a meeting, or notify of an upcoming meeting). The other task the trayapp has is to use a custom protocol (trayapp://) to perform some ajax calls back to the server.

ASP.NET jQuery Ajax Calling Code-Behind Method

I am very new to web development, but have a lot of experience in development in general. I have an ASP page that has a few input fields and a submit button. This submit button purely calls $.ajax, which I intended to have call a method in the code-behind file. However, I’ve noticed two interesting things. First, the ajax call succeeds regardless of what data is provided to it. Secondly, the responseText field is the entire page’s html source.