A smartcard includes a fingerprint sensor and a detector circuit comprising at least first and second electrodes that are insulated from each other and that form an open circuit. The first electrode and the second electrode is arranged in such a manner that. When a user applies a first finger on the fingerprint sensor and uses a second finger to grip the smartcard, the first finger contacts the first electrode and the second finger contacts the second electrode so as to form a loop that closes the open circuit. The detector circuit further comprises a filter circuit connected to the first electrode and to the second electrode, a generator arranged to generate first signals across the terminals of the filter circuit, and processor means arranged to acquire second signals and, from the second signals, to detect whether the first and second fingers include a fake finger.