An accessory device for a physically separate audio device, wherein the accessory is configured to be connected to the physically separate audio device, the accessory comprising: at least one earpiece unit (204A, 204B, 600, 700, 800), each comprising an audio transducer configured to provide sound to a user and at least one optical radiation source (212A, 212B) configured to provide optical radiation to the user; a first communication interface; a second communication interface configured to receive an electrical audio signal from the physically separate audio device and to transmit identification information of the accessory to the separate audio device; a controller operatively coupled to the first communication interface and to the second communication interface, wherein the controller is configured to forward the electrical audio signal received from the second communication interface to the first communication interface; first signal conveyer (208A, 208B) coupled to the first communication interface and configured to convey the electrical audio signal to each audio transducer (206A, 206B) in order to drive the audio transducer (206A, 206B), wherein the first communication interface is configured to output the electrical audio signal to the first signal conveyer (208A, 208B); and second signal conveyer (214A, 214B) coupled to the first communication interface and configured to convey at least one electrical optic signal to the at least one optical radiation source (212A, 212B) in order to drive the at least one optical radiation source (212A, 212B), wherein the second signal conveyer (214A, 214B) is different from the first signal conveyer (208A, 208B), wherein the controller is further configured to generate and provide the at least one electrical optic signal for driving the at least one optical radiation source (212A, 212B) to the first communication interface; and characterised in that the first communication interface is further configured to output the received at least one electrical optic signal to the second signal conveyer (212A, 212B) and to output the received electrical audio signal to the first signal conveyer (208A, 208B). at least one earpiece unit (204A, 204B, 600, 700, 800), each comprising an audio transducer configured to provide sound to a user and at least one optical radiation source (212A, 212B) configured to provide optical radiation to the user; a first communication interface; a second communication interface configured to receive an electrical audio signal from the physically separate audio device and to transmit identification information of the accessory to the separate audio device; a controller operatively coupled to the first communication interface and to the second communication interface, wherein the controller is configured to forward the electrical audio signal received from the second communication interface to the first communication interface; first signal conveyer (208A, 208B) coupled to the first communication interface and configured to convey the electrical audio signal to each audio transducer (206A, 206B) in order to drive the audio transducer (206A, 206B), wherein the first communication interface is configured to output the electrical audio signal to the first signal conveyer (208A, 208B); and second signal conveyer (214A, 214B) coupled to the first communication interface and configured to convey at least one electrical optic signal to the at least one optical radiation source (212A, 212B) in order to drive the at least one optical radiation source (212A, 212B), wherein the second signal conveyer (214A, 214B) is different from the first signal conveyer (208A, 208B), wherein the controller is further configured to generate and provide the at least one electrical optic signal for driving the at least one optical radiation source (212A, 212B) to the first communication interface; and characterised in that the first communication interface is further configured to output the received at least one electrical optic signal to the second signal conveyer (212A, 212B) and to output the received electrical audio signal to the first signal conveyer (208A, 208B).