diff --git a/client/dcwebui.js b/client/dcwebui.js
index 7b0ac18..2dab036 100644
--- a/client/dcwebui.js
+++ b/client/dcwebui.js
@@ -396,6 +396,42 @@ var submit = function() {
 	$("#chatbox").value = '';
 };
 
+/* page visibility */
+
+var pagevis_currently_visible = true;
+
+var pagevis_setup(fnActive, fnInactive) {
+	
+	var h, visibilityChange; 
+	if (typeof document.hidden !== "undefined") { // Opera 12.10 and Firefox 18 and later support 
+		h = "hidden";
+		visibilityChange = "visibilitychange";
+	} else if (typeof document.msHidden !== "undefined") {
+		h = "msHidden";
+		visibilityChange = "msvisibilitychange";
+	} else if (typeof document.webkitHidden !== "undefined") {
+		h = "webkitHidden";
+		visibilityChange = "webkitvisibilitychange";
+	}
+
+	// Warn if the browser doesn't support addEventListener or the Page Visibility API
+	if (typeof document[h] === "undefined") {
+		// Browser doesn't support Page Visibility API
+		// Behave as if the page is always visible.
+		pagevis_currently_visible = true
+		fnActive();
+		
+	} else {		
+		document.addEventListener(visibilityChange, function() {
+			if (document[h]) {
+				fnInactive();
+			} else {
+				fnActive();
+			}
+		});
+	}
+}
+
 /* tabs */
 
 /**
@@ -929,6 +965,17 @@ window.onload = function() {
 	
 	tab_addHandlers();
 	
+	pagevis_currently_visible(
+		function() {
+			// We've just become active
+			// If the foreground is a PM window with UNREAD, mark it as read
+		},
+		function() {
+			// We've just become inactive
+			// ...TODO
+		}
+	);
+	
 	// Hacks for WiiU user-agent
 	
 	if (navigator && navigator.userAgent && !!navigator.userAgent.match("Nintendo WiiU")) {