The invention relates to a procedure for accessing a non-volatile watch memory, the watch comprising two supply terminals accessible from the outside that define a potential difference corresponding to a standard supply voltage, and a control circuit of the non-volatile memory produced using a technology supporting a predefined maximum supply voltage, the access procedure consisting of transmitting the following to the control circuit of the non-volatile memory by means of a supply terminal of the watch: a) an opening key to authorize access to the non-volatile memory; b) an instruction for access to the non-volatile memory; the procedure being characterized in that the opening key is a predefined instruction transmitted by modulation of the standard supply voltage such that this does not exceed the predefined maximum supply voltage.