There is disclosed a portable
electronic instrument (1) including a case (2) and a
user interface (11 to 15) for selecting the functions of said portable
electronic instrument, this
user interface including at least a first control member (11) mounted to be mobile in an
assembly orifice (3a) arranged in the case so as to have a translation travel along an axis of actuation (X—X), said control member being able to be actuated by pressure to be brought from a position called the non pushed-in position to a position called the pushed-in position and to generate in response a
control signal (SEL). The control member includes an
electrically conductive stem (100) which passes through the
assembly orifice and which includes first and second ends opening out respectively inside and outside the case, said stem being adapted to allow transmission of electric signals from and / or to the portable
electronic instrument, when the control member is brought into said pushed-in position. This electronic instrument further includes means (3, 30, 40; 35, 40) for bringing the stem of the control member to a determined
electric potential when the control member occupies the non pushed-in position and for interrupting the connection of the stem of the control member to the determined
electric potential when the control member occupies said pushed-in position and for thus allowing transmission of said electric signals from and / or to the portable electronic instrument.