Do I always have to authenticate on all my devices while using Google Authenticator?
Like any other form of multi-factor authentication, you can 'trust' certain computers or devices you deem secure, and you will not be required to authenticate using Google Authenticator. The next time you login, when the Google Authenticator dialog comes up, you will see an option to select "This computer is trusted, do not require a second form of authentication." This dialog also presents you an option to name the trusted device. After trusting a device, you will no longer need to authenticate using Google Authenticator when you login on that particular device within 30 days. You can view these trusted devices under your Account Settings > Trusted Devices.