Trusted Devices is an extra layer of security for your TeamViewer account. As a preventive measure to ensure your account's security, you need to authorize every new device on which you sign in to your account for the very first time.
How it works:
After signing in to the Blizz client with your account credentials on a new device for the first time, a pop-up appears.
A sign-in confirmation email is sent to the email address of your Blizz account.
Click the link within the sign-in confirmation email, to authorize the device. The new device is now a trusted device.
Note: the link in this email is only valid for 30 minutes. If the link expires, you will need to sign into your account once more on the new device, so that a new authorization email can be generated
A message is displayed in the Management Console informing you that the new device is now a trusted device.
Once you complete the authorization process, you are able to sign in on the new device with your Blizz account credentials.
As an alternative to the Trusted Devices authorization process, you can enable two-factor authentication on your account instead. If you are using two-factor authentication, then the Trusted Devices authorization email won’t be required anymore when you sign into your account on a new device.
You can find more information about two-factor authentication here.