The device integrates, on a synthetic material foil, a system for detecting the action of keys of a keyboard and a homogeneous illumination system for the keyboard. A film 10 is folded into two parts 11 and 12. Domes 13 are preformed on the upper part 11 and a detection circuit 16 is printed on the lower part 12. Contact electrodes 15 are fixed under each dome 13 so as to realize an electric contact with the detection circuit 16 when the dome 13 is pressed by means of a key 22 of the keyboard 20. The keys of the keyboard are illuminated by an electroluminescent ink 17 between the domes 13, deposited on a plane surface 18 of the upper part 11 of the synthetic material foil 10.