Quick guide to add gem invisible_captcha to your devise registrations.

Why? For fewer bots to sign up!

Final result:

captcha1

captcha2

HOWTO

gemfile:

gem 'invisible_captcha'

console:

bundle
rails g devise:controllers users -c=registrations

app/controllers/users/registrations_controller.rb

class Users::RegistrationsController < Devise::RegistrationsController
  invisible_captcha only: [:create]

routes.rb:

  devise_for :users, controllers: {
    registrations: 'users/registrations'
  }

app/views/devise/registrations/new.html.erb, inside the form:

<%= invisible_captcha %>

Alternative wiki to install Google REcaptcha gem