The breathalyser uses an electrochemical fuel cell to measure the alcohol concentration from the sample of the expired breath from an individual (in this case – the driver). If alcohol is present, a corresponding voltage is generated from the fuel cell, which is proportional to the alcohol content of the sample provided. After that, the voltage level is converted to BAC respectively, which is then displayed. For a convenient power supply, it can be connected to a vehicle cigarette adaptor.