migration.rb

class AddDeviseLockableColumnsToUser < ActiveRecord::Migration
  def change
    change_table :users do |t|
      t.lockable :maximum_attemps => 3, :lock_strategy => :failed_attempts, :unlock_strategy => :none
    end
  end
end

user.rb

class User < ActiveRecord::Base
  # Include default devise modules. Others available are:
  # :token_authenticatable, :confirmable,
  # :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable, :lockable

  # Setup accessible (or protected) attributes for your model
  attr_accessible :email, :password, :password_confirmation, :remember_me
  # attr_accessible :title, :body
end