Project Summary/Abstract The availability of wearable biosensors that continuously and/or remotely monitor alcohol use is increasing and has created new opportunities for research and intervention in clinical practice and forensic settings. Our previous work in this area has focused on transdermal alcohol monitors, which remotely and continuously monitor alcohol excreted through the skin. While such devices, like Secure Continuous Remote Alcohol Monitors, have been validated and found reliable, they have some disadvantages that limit widespread adoption including availability, cost, size, interference with physical activities, and stigma. One alternative is the use of breathalyzers that remotely sample and report breath alcohol levels across the day. These are becoming the preferred method for monitoring alcohol use in settings where continuous monitoring for alcohol consumption is required. Although remote breathalyzers are accurate for detecting current blood alcohol levels and identifying the individual providing the sample through facial recognition, their primary limitation could be the failure to detect drinking when monitoring is absent during the "off- cycle”; the 10 hours between early 9pm and 6am when heavy alcohol use could occur. Individuals who have difficulty remaining abstinent and may adopt a pattern of drinking during “off-cycle” periods to avoid the negative consequences associated with positive breath samples. We propose that current practices for remote alcohol breath monitoring in research, clinical, and judicial settings are inadequate to detect drinking. Specifically, we aim to evaluate the accuracy of remote breath alcohol monitoring to detect drinking events; and determine if drinking undetected by remote breath alcohol monitoring can be identified by phosphatidylethanol measurement. We expect that breath alcohol monitoring (and infrequent blood spot sampling) will be more acceptable than transdermal alcohol monitoring. This work challenges current practices by providing evidence of “off-cycle” drinking (Aim 1) and will improve existing methods by validating remote breath testing plus periodic measures of phosphatidylethanol (Aim 2). We also will determine the optimal frequency of phosphatidylethanol measurements to confidently confirm abstinence or identify those who may be motivated to adopt patterns of drinking to avoid detection and consequences (Aim 2). This work will help redefine remote alcohol-use monitoring procedures and significantly improve clinical, forensic and research practices.