Google's reCAPTCHA can tell you're not a bot from your phone
 

Google's reCAPTCHA has evolved from distorted text, to street numbers, to "I'm not a robot" tickboxes and, most recently, to their new invisible system. And now the company is bringing its bot-fighting program to Android.

https://www.engadget.com/2017/06/09/...ptcha-android/