Yahoo Account Key sends a notification that you accept on your push-enabled mobile device to access your account, instead of using a password. You can associate multiple devices per account to get this notification.
During a security review, you’ll see a list of all associated devices that can get this notification so that you can review and control which devices can grant access to your account.
We strongly suggest that you disconnect unfamiliar, old, or unused devices by clicking Sign out beside the device. You can also review your recent activity at any time to review this information.