A few months after Titan Security Key's acquisition, Google has decided to give all Android smartphone owners with version 7.0 or later the ability to use them as security keys to login to its services.
Essentially, this is an attempt to extend the famous two-factor authentication (2FA) or two-step verification (2SV) with the easiest solution for users, that of their smartphone. Physical security keys may cost a little, but it is inconvenient for the user to always carry them with him.
Setting up Android smartphone as a security key is done through Google Play Services. Once the process is complete, it is possible to use your smartphone for this job as long as you have Bluetooth enabled, for example. on your laptop and your device. From there on, you can sign in to your Google Account and authenticate it by clicking on the command displayed on your smartphone screen.
More about the process can be found here.