time out a user session via devise after 10 minutes of inactivity

app/models/user.rb

@@ -14,7 +14,8 @@ class User
   plugin MongoMapper::Devise
 
   devise :invitable, :database_authenticatable, :registerable,
-         :recoverable, :rememberable, :trackable, :validatable
+         :recoverable, :rememberable, :trackable, :validatable,
+         :timeoutable
 
   key :username
   key :serialized_private_key, String

config/initializers/devise.rb

@@ -80,7 +80,7 @@ Devise.setup do |config|
   # ==> Configuration for :timeoutable
   # The time you want to timeout the user session without activity. After this
   # time the user will be asked for credentials again.
-  # config.timeout_in = 10.minutes
+  config.timeout_in = 10.minutes
 
   # ==> Configuration for :lockable
   # Defines which strategy will be used to lock an account.