  Non-invasive continuous alcohol monitoring has potential applications in both
population research and in clinical management of acute alcohol intoxication or
chronic alcoholism. Current wearable monitors based on transdermal alcohol
content (TAC) sensing are relatively bulky and have limited quantification
accuracy. Here we describe the development of a discreet wearable transdermal
alcohol (TAC) sensor in the form of a wristband or armband. This novel sensor
can detect vapor-phase alcohol in perspiration from 0.09 ppm (equivalent to
0.09 mg/dL sweat alcohol concentration at 25 {\deg}C under Henry's Law
equilibrium) to over 500 ppm at one-minute time resolution. The TAC sensor is
powered by a 110 mAh lithium battery that lasts for over 7 days. In addition,
the sensor can function as a medical "internet-of-things" (IoT) device by
connecting to an Android smartphone gateway via Bluetooth Low Energy (BLE) and
upload data to a cloud informatics system. Such wearable IoT sensors may enable
large-scale alcohol-related research and personalized management. We also
present evidence suggesting a hypothesis that perspiration rate is the dominant
factor leading to TAC measurement variabilities, which may inform more
reproducible and accurate TAC sensor designs in the future.
