A method for transmitting data from an electronic device to an electronic watch, including the following steps: emitting a sequence of light signals with a light source of the electronic device, each signal having a light-intensity level belonging to a set of at least four light-intensity levels, said sequence corresponding to a code of the data to be transmitted; detecting successive light-intensity levels with a phototransistor of the watch, so as to reconstitute the sequence; and decoding the sequence in order to reconstitute the data, the set of at least four intensity levels being divided into a first portion and a second portion, one light signal in two of the sequence having a light-intensity level belonging to the first portion, the other signals having a light-intensity level belonging to the second portion.