The STK25MI is the diaphragm type prepaid gas meter based on the STK25MT which is the well matured smart gas meter and long seller for more than a quarter century in Japan. The STK25MI works as a normal diaphragm gas meter with several safety functions for post-pay use. The highlight of the STK25MI is the prepaid function with the embedded NFC card reader/writer. In combination with POS terminals, the Pre-Pay gas system is easily installed.