A stacked battery sealed by a film casing shows a raised degree of resistance against vibrations. The system comprises a plurality of call units arranged to be accessible for the callers and each having a handset for carrying out calls, a personal identification means for identifying any caller; and a camera enabling observation of the callers. The dimension of the electrode patterns is increased by extending the width of the first electrode pattern to correspond to the length of the first slit, and the first and second electrode patterns form the successive resonant length via the second slit.