A secure optical data disc comprising an electronic article surveillance tag embedded within a layered disc structure comprising first and second substrates is disclosed. The separator unit includes a sheet-shaped gas barrier member, which blocks a gas, and a collector, which is inserted between the gas barrier member and the fuel electrode or the oxygen electrode and which is provided with a plurality of openings that diffuse the gas. In this way, each user equipment is given some knowledge of the state of the buffer in the other user equipments. The first mechanism is adapted to generate a first physical address from the virtual address in response to receiving the first signal, and the second mechanism is adapted to generate a second physical address from the virtual address in response to receiving the second signal. The extension is hollow with an open end for being removably secured to the one end as a first cap. Said device is also provided with a radiation source and a receiver-transducer of physical fields and a packer.