The invention concerns a contactless portable object (10, 30, 60) featuring a main radiofrequency device made up of a main chip (18, 38, 68) and a main antenna (16, 36, 66) connected together so that, when the portable object enters the magnetic field of a suitable reader, the main radiofrequency device provides power to the chip and ensures communication between the chip and the reader. According to the main characteristic of the invention, the portable object includes a secondary contactless device featuring a secondary antenna (12, 32, 62) and an electric circuit set up in such a way that, when the two antennas enter the magnetic field of a suitable reader at the same time, the amount of energy required to power the electric circuit and have it operational being less than the amount of energy required to power the main chip (18, 38, 68) and have it operational, the electric circuit is powered and makes the reading of data of the main chip impossible.