How to know when the window of my application is closed?

Hi, I would like to run a function when I close the window of my application. For example, imagine that what I would like to do is to open a new window when I close the window of my application. (This is just a example of a function to test my problem) The code would look like this: Response.Write(""); I tried many solutions, but I haven't found yet anyone that works. If I put this code in the PAGE_UNLOAD event, this would fire everytime that the page refresh, and this means that a new window is opened everytime I click on a button, select in a dropdownlist and so.... If I put the code in the PAGE_DISPOSED event, or in the SESSION_ENDS or APPLICATION_ENDS of the Global.asax.cs file, the code is not executed so the new window is not opened when closing my application. After this, I tried to put that between the tags or

of the HTML code, for example like this: With "ONUNLOAD" I got the same result as in "Page_Unload", and with the rest of the events that I tried ("ONDRAG", "ONDRAG", ...) nothing is executed, so the new window is not opened. I also tried "ONCLOSE", but this event is not recognized, and the window is not opened neither. The code is OK, because the code is properly executed when using the Page_unLoad event or the HTML code with onunload, the problem is to find WHEN or HOW does it recognise that the window is closed. Thanks, goraperas