How to detect that Ctrl+R was pressed?

You have to use the keydown function to trap Ctrl characters. Here is my implementation of Ctrl+A:

    $(document).keydown(function(e) {
        if (e.keyCode == 65 && e.ctrlKey) {
            alert('ctrl A');
        }
    });

Ctrl-R is tougher because in most browsers, that is Reload Page, which means the javascript doesn't run, the page is refreshed.

Just a note as well, the keyCode value are different in the keydown/keyupup functions than in the keypress functions.

EDIT: Removed ctrl variable, forgot about ctrlKey

Here is an entire list of keycodes that you can use.

This is the code I'm using to disable refresh on IE and firefox (This works well for F5, Ctrl+F5 and Ctrl+R)

<script language="javascript" type="text/javascript">
    //this code handles the F5/Ctrl+F5/Ctrl+R
    document.onkeydown = checkKeycode
    function checkKeycode(e) {
        var keycode;
        if (window.event)
            keycode = window.event.keyCode;
        else if (e)
            keycode = e.which;

        // Mozilla firefox
        if ($.browser.mozilla) {
            if (keycode == 116 ||(e.ctrlKey && keycode == 82)) {
                if (e.preventDefault)
                {
                    e.preventDefault();
                    e.stopPropagation();
                }
            }
        } 
        // IE
        else if ($.browser.msie) {
            if (keycode == 116 || (window.event.ctrlKey && keycode == 82)) {
                window.event.returnValue = false;
                window.event.keyCode = 0;
                window.status = "Refresh is disabled";
            }
        }
    }
</script>

If you don't want to use useragent to detect what type of browser it is ($.browser uses navigator.userAgent to determine the platform), you can use

if('MozBoxSizing' in document.documentElement.style) - returns true for firefox