You need a captcha tool in your app.

Why? For fewer bot sign-ups!

You don't need Google Recaptcha in your app:

Instead - try an open source Ruby alternative!

Quick guide to add gem invisible_captcha to your devise registrations:

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 %>

That's it! And no dependency on external API!

Alternative wiki to install Google REcaptcha gem