Continuous transdermal alcohol monitoring may be useful for self-tracking \cite{Gimpe2013,Pfeiffer2016-um,Lupton_2016}, medicine \cite{Indig_2008,Kim_2019}, remote monitoring of alcohol use \cite{Alessi_2019,Gordon_2017}, traffic safety \cite{Webster2007}, law \cite{Robertson2006-lb}, and research \cite{Alessi_2017,Wang_2019}. Most of the current generation of transdermal alcohol monitoring biosensors are bulky devices marketed towards criminal law enforcement for the monitoring of repeat alcohol-related offenses \cite{Marques_2009,Roache_2015,Marques2007-mb,McKnight2012-ar,Alessi_2017}. More recently, discrete transdermal alcohol sensors have been developed for continuous monitoring of alcohol use \cite{Hair2019-rq,Lansdorp2019-kt,Campbell2018-ug,Kim_2016,Gamella_2014,Mohan_2017,Lawson_2017,Carter_2020,Umasankar_2016}

Methods and Materials

The BACtrack® Skyn™ (BACtrack Breathalyzers, San Fransisco, California, USA) device contains an electrochemical fuel cell to continuously monitor alcohol vapors emanating from the skin. It records measurements every 20 seconds and transmits data via Bluetooth® to an app on the user's smartphone. Photos of the device are shown in figures \ref{365666} and \ref{168024}.