Abstract: An electronic film (E-film) apparatus that reversibly converts a conventional film camera body into an E-film camera is described. The electronic film apparatus includes one or more state sensors that sense the operating state of the camera body. State sensors include an electromagnetic sensor, an acoustic sensor, and/or an optical sensor. The data gathered by the sensors is used to determine the operating state of the camera. Based on the operating state of the camera, the E-film apparatus operates in various power modes, including sleep modes, low power modes, and full power modes. The electromagnetic sensor includes a loop or coil that converts electromagnetic fields into an electrical signal. The acoustic sensor senses vibrations in the camera due to operation of the mechanical aspects of the camera body. The acoustic sensor converts vibrations in the camera body into an electrical signal.