A handheld communications device for transmitting an encryption key is provided. The device comprises a display device, and a data processor. The data processor of the handheld communications device is in communication with the display device. The data processor is configured to generate an encryption key, and to vary a visual output of the display device over time in accordance with a bit sequence of the encryption key. The varying visual output comprises a sequence of colors and/or brightness levels output by the display device.