Disclosed are various embodiments for using an audio interface device to facilitate authentication for other devices. An authentication service causes a first client device to present an authentication code via an output device of the first client device. The authentication service receives the authentication code from a second client device. The second client device is in an authenticated state for access to an account, and the second client device received the authentication code from an environmental sensor while in a listening mode. The authentication service authenticates the first client device for access to the account in response to determining that the authentication code received from the second client device matches the authentication code presented by the first client device.