How to automatically reload a page after a given period of inactivity

If you want to refresh the page if there is no activity then you need to figure out how to define activity. Let's say we refresh the page every minute unless someone presses a key or moves the mouse. This uses jQuery for event binding:

<script>
     var time = new Date().getTime();
     $(document.body).bind("mousemove keypress", function(e) {
         time = new Date().getTime();
     });

     function refresh() {
         if(new Date().getTime() - time >= 60000) 
             window.location.reload(true);
         else 
             setTimeout(refresh, 10000);
     }

     setTimeout(refresh, 10000);
</script>

This can be accomplished without javascript, with this metatag:

<meta http-equiv="refresh" content="5" >

where content ="5" are the seconds that the page will wait until refreshed.

But you said only if there was no activity, what kind for activity would that be?

I have built a complete javascript solution as well that does not require jquery. Might be able to turn it into a plugin. I use it for fluid auto-refreshing, but it looks like it could help you here.

JSFiddle AutoRefresh

// Refresh Rate is how often you want to refresh the page 
// bassed off the user inactivity. 
var refresh_rate = 200; //<-- In seconds, change to your needs
var last_user_action = 0;
var has_focus = false;
var lost_focus_count = 0;
// If the user loses focus on the browser to many times 
// we want to refresh anyway even if they are typing. 
// This is so we don't get the browser locked into 
// a state where the refresh never happens.    
var focus_margin = 10; 

// Reset the Timer on users last action
function reset() {
    last_user_action = 0;
    console.log("Reset");
}

function windowHasFocus() {
    has_focus = true;
}

function windowLostFocus() {
    has_focus = false;
    lost_focus_count++;
    console.log(lost_focus_count + " <~ Lost Focus");
}

// Count Down that executes ever second
setInterval(function () {
    last_user_action++;
    refreshCheck();
}, 1000);

// The code that checks if the window needs to reload
function refreshCheck() {
    var focus = window.onfocus;
    if ((last_user_action >= refresh_rate && !has_focus && document.readyState == "complete") || lost_focus_count > focus_margin) {
        window.location.reload(); // If this is called no reset is needed
        reset(); // We want to reset just to make sure the location reload is not called.
    }

}
window.addEventListener("focus", windowHasFocus, false);
window.addEventListener("blur", windowLostFocus, false);
window.addEventListener("click", reset, false);
window.addEventListener("mousemove", reset, false);
window.addEventListener("keypress", reset, false);
window.addEventListener("scroll", reset, false);
document.addEventListener("touchMove", reset, false);
document.addEventListener("touchEnd", reset, false);