A method for transmitting data from an electronic device to an electronic watch is provided, including emitting a first sequence of light signals with a first light source of the device at a light-intensity level among at least four light-intensity levels, the emitted first sequence corresponding to a code of data to be transmitted; emitting a second sequence of light signals at two light-intensity levels corresponding to clock phases, simultaneously to the emitted first sequence, with a second light source of the device; detecting successive light-intensity levels with a first phototransistor of a watch, to reconstitute a sequence of data; detecting a succession of the two light-intensity levels with a second phototransistor of the watch, to reconstitute the clock phases, the first and the second sequences emitted at two distinct wavelengths; and decoding the sequence of data by a sequence of the clock phases to reconstitute the data.