Index: config/routes.rb
===================================================================
--- config/routes.rb	(revision 12244)
+++ config/routes.rb	(working copy)
@@ -17,6 +17,8 @@
 
 RedmineApp::Application.routes.draw do
   root :to => 'welcome#index', :as => 'home'
+  
+  get 'session_heartbeat', :to => 'application#session_heartbeat'
 
   match 'login', :to => 'account#login', :as => 'signin', :via => [:get, :post]
   match 'logout', :to => 'account#logout', :as => 'signout', :via => [:get, :post]
Index: public/javascripts/application.js
===================================================================
--- public/javascripts/application.js	(revision 12244)
+++ public/javascripts/application.js	(working copy)
@@ -591,3 +591,18 @@
 $(document).ready(setupAjaxIndicator);
 $(document).ready(hideOnLoad);
 $(document).ready(addFormObserversForDoubleSubmit);
+
+function SessionHeartbeat() {
+    $.ajax( {
+            url: '/session_heartbeat',
+            success: function(data) {                                
+                if(data.expired) {
+                    alert(data.message);                       
+                }
+                else if(data.remain > 0) {
+                    setTimeout(SessionHeartbeat, data.remain);
+                }
+            }             
+        }
+    );        
+}
\ No newline at end of file
Index: app/controllers/application_controller.rb
===================================================================
--- app/controllers/application_controller.rb	(revision 12244)
+++ app/controllers/application_controller.rb	(working copy)
@@ -48,7 +48,28 @@
   include Redmine::MenuManager::MenuController
   helper Redmine::MenuManager::MenuHelper
 
+  def session_heartbeat
+    remain = 0
+    if Setting.session_lifetime? && session[:ctime]
+      remain = (Setting.session_lifetime.to_i * 60) - (Time.now.utc.to_i - session[:ctime].to_i)          
+    end
+    if Setting.session_timeout? && session[:atime]
+      if remain > 0
+        remain = [remain, (Setting.session_timeout.to_i * 60) - (Time.now.utc.to_i - session[:atime].to_i)].min
+      else
+        remain = (Setting.session_timeout.to_i * 60) - (Time.now.utc.to_i - session[:atime].to_i)
+      end          
+    end                
+    if session_expired? || remain <= 0                
+      render json: { expired: true, message: l(:error_session_expired) }
+    else                        
+      render json: { expired: false, remain: (remain * 1000) }
+    end
+  end
+
   def session_expiration
+    # Skip session heartbeat
+    return if ((params[:controller] == 'application') && (params[:action] = 'session_heartbeat'))
     if session[:user_id]
       if session_expired? && !try_to_autologin
         reset_session
Index: app/helpers/application_helper.rb
===================================================================
--- app/helpers/application_helper.rb	(revision 12244)
+++ app/helpers/application_helper.rb	(working copy)
@@ -1227,6 +1227,14 @@
     unless User.current.pref.warn_on_leaving_unsaved == '0'
       tags << "\n".html_safe + javascript_tag("$(window).load(function(){ warnLeavingUnsaved('#{escape_javascript l(:text_warn_on_leaving_unsaved)}'); });")
     end
+    if User.current && (!User.current.anonymous?) && (Setting.session_timeout || Setting.session_lifetime)
+      lifetime = Setting.session_lifetime ? Setting.session_lifetime.to_i : 0
+      timeout = Setting.session_timeout ? Setting.session_timeout.to_i : 0
+      timeout = lifetime if lifetime > 0 && lifetime < timeout      
+      unless timeout == 0
+        tags << "\n".html_safe + javascript_tag("setTimeout(SessionHeartbeat, #{timeout * 60000});")
+      end
+    end
     tags
   end