A novel authentication system is provided. In addition, a method for recording an unlocking history is provided. The authentication system includes an arithmetic device and an input/output device. The arithmetic device supplies first control data and second control data, and is supplied with a sensor signal. The input/output device includes an electric lock and a reading portion, and the electric lock is unlocked on the basis of the second control data. The reading portion is supplied with the first control data, supplies the sensor signal, and includes a light-emitting element and a pixel array. The light-emitting element emits light including infrared rays, the pixel array includes pixels, the pixels each include an imaging circuit and a photoelectric conversion element, the imaging circuit is electrically connected to the photoelectric conversion element, the imaging circuit includes a transistor, and the transistor includes an oxide semiconductor film.