“…Nowadays, realtime monitoring of multiple air pollutants, for example, volatile organic compounds (VOCs), SO , X NO , X CO, etc is essential to maintain healthy conditions. [5][6][7][8][9][10] For example, Palomeque-Mangut, et al have developed WHD that can measure outdoor air quality and send the data to the user through Bluetooth Low Energy (BLE) which is small-sized, light-weighted, and belt-worn, with a userfriendly interface. 11 The other research groups have reported a WHD that can detect toxic gases such as CH , 4 O , 2 SO , 2 and NO 2 by implementing electrochemical gas sensor arrays.…”