the duration test is satisfied and a decision step step 61 verifies whether the instantaneous variations of the slopes das fig3 at the ends a and b have a value in absolute value greater than predetermined threshold values for example 5 in relative values variations das at the point a lower than u2212 5 and at the point b higher than 5 in the example a final test decision step 63 involves the monitoring by a ratio u201c r u201d defining the variation amplitude of the signal between a point of critical change in instantaneous inclination and a current point divided by the unit of time by dividing by the number of measurement points made during this variation if the ratio r is less than a predefined threshold value rmin 1 5 in the example the response u201c no u201d sends the process back to the start step 41 however if the ratio r remains higher than the pre established value rmin the selected form is provisionally validated at the step 65 which corresponds to the validation step 23 v in fig4 the selected form appears on each signal and the simultaneity criterion is subsequently applied to this pair of forms as explained hereinabove with regard to fig4 if the pair of forms selected satisfies this simultaneity criterion its validation is confirmed and the remote access system is made secure in addition the coherence criterion for amplitudes of the selected forms pair such as described with regard to fig4 may subsequently be applied in order to reinforce the validation as needs be the invention is not limited to the exemplary embodiments described and shown the remote access system can comprise more than one pair of sensors for example two or even three pairs or.