In the simplest terms, the atm machine has a bill checking module in it (equivalent to a bill checker). How is the crown number recorded? The module has a camera (should be called image sensor), every money over the crown number of the place photographed, and then processed, converted to text stored, (of course, can also be printed on the voucher) there is no unknown secret, as you use the atm is to change the hardware or update the software in order to achieve the effect that depends on the previous atm what is the situation. The People's Bank of China stipulates that by the end of the year 14 all atm must have the function of recording the crown number, so some machines do not print on the voucher but will also retain the data. As for the monitoring of the flow of RMB you said, you can query the banknotes to the city level, and then down to check the words, theoretically it can be achieved, the actual operation of the difficulty is too large and meaningless.