A trusted device, such as a wristwatch 2, is provided with authentication circuitry 26, used to perform an authentication operation to switch the trusted device into an authenticated state. Retention monitoring circuitry 32 monitors the physical possession of the trusted device by the user following the authentication operation and switches the trusted device out of an authenticated state if the trusted device does not remain in the physical possession of the user. While the trusted device remains in the physical possession of the user, communication triggering circuitry 38 is used to detect a request to establish communication with a target device that is one of a plurality of different target devices and communication circuitry 40 is used to communicate with that target device using an authenticated identity of the user.