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.