The magnetic control device (1) for a timepiece comprises a sealed tube (3) which comprises a blind end inserted into an opening of the timepiece, whereas the other end of the tube opens towards the outside. A control stem (12) is provided in order to slide inside the tube (3). It carries a magnet (21) which is displaced integrally with the stem inside the tube. By manipulating the end of the stem which emerges from the tube (3), the wearer of the watch can make the magnet selectively occupy three positions. A first and a second magnetic sensor (22, 23) with two states are disposed inside the timepiece along the sealed tube so that three different combinations of a state of the first sensor (22) with a state of the second sensor (23) are respectively associated with three predefined positions of the first magnet (21).