Abstract: An on-board telematic device intended to be attached to a metal part (3) of a body of a motor vehicle comprises, according to the invention, a housing (1) integrating a printed circuit board (5), a face of which supports at least one electronic power component (6), a radiofrequency antenna (7), intended to extend through an opening of the metal part (3), and a metal screen (9) interposed between a lower part of the antenna (7), on the one hand, and the printed circuit board (5) and said at least one component, on the other hand, in order to isolate the antenna from parasitic emissions. The component (6) is placed in line with the metal screen (9) and in thermal contact with a portion of said screen, and said screen (9) is made of a thermally conductive material so as to form a thermal transfer means between the electronic power component (6) and the metal part (3).