Towards a Wearable Alcohol Biosensor: Examining the Accuracy of BAC Estimates From New-Generation Transdermal Technology Using Large-Scale Human Testing and Machine Learning Algorithms

Laboratory Procedures: The aim of the laboratory study is to capture variability in the TAC-BAC relationship across individuals in a controlled context, featuring manipulations theorized to confound transdermal measurements of BAC and so ensuring adequate variability in these factors in the broader dataset. Laboratory alcohol-administration sessions will be held at one-week intervals, scheduled at study initiation (day 0), study midpoint (day 7), and study end (day 14).

Alcohol-administration procedures will employ a within (alcohol dose) X between (rate of consumption) participant design. All participants will consume three doses of alcohol over the course of the three laboratory sessions, targeting peak blood alcohol concentration (BAC) levels of .03%, .06%, and .09% respectively. The order of alcohol doses will be counterbalanced across participants. The exact quantity of alcohol administered to each participant in order to achieve these target peak BACs will be calculated based on individualized formulas adjusting for drinking rate, sex, height, weight, and age (see formulas provided in Watson et al., (1981)). Rate of consumption will be manipulated between participants, with equal numbers of participants assigned to consume alcohol at relatively "fast" and "slow" rates. Beverage intake will be monitored to ensure participant comfort and even consumption across the beverage administration period. After beverage administration, participants will provide breath alcohol concentration (BrAC) readings at 10- min intervals.

In addition, during the laboratory procedures, participants will be exposed to environmental factors that are known to impact readings taken by transdermal sensors. These manipulations will allow the research team to train the machine learning algorithm to recognize and model for these environmental effects. These manipulations include: 1) Environmental alcohol: common household products containing alcohol (e.g., hand sanitizer, perfume, lotion containing alcohol) will be sprayed or applied in proximity to the transdermal sensor; 2) Sweating: Participants will be asked to engage in a brief 10-30 minute aerobic exercise while in a seated position (i.e., stationary biking) while under the supervision of a research assistant. This brief exercise will be designed simply to yield exertion to the point of sweating and not exertion beyond this point; 3) Arm Movements: Participants will be asked to engage in isolated body movements (e.g., arms and feet) to determine whether device shifting caused by such movements impact readings taken by transdermal sensors.

Ambulatory Procedures: This arm of the study aims to capture the TAC-BAC relationship among participants drinking in everyday settings. Ambulatory assessment will take place over 14 days. During laboratory session 1, prior to beverage administration, participants will be oriented to ambulatory study procedures. One or more transdermal device will be worn throughout participation. During orientation, participants will be trained to use the mobile breathalyzer. To avoid contamination of breathalyzer readings by mouth alcohol, participants will be instructed to wait 5 minutes after their last sip of alcohol to provide a reading. Also during this orientation session, participants will receive training in standard drink reporting (used to validate breathalyzer readings). During ambulatory assessment, participants will provide breathalyzer readings in response to both random and user-initiated prompts via their smartphones. On day 14 of the study, participants will attend a final laboratory session during which they will return study equipment as well as complete questionnaires asking them to reflect on their experience using the transdermal sensors and their likelihood to adopt a transdermal sensor application.

Since initial record creation, the study start date has been updated to conform to current ICMJE pre-registration requirements. Only participants recruited subsequent, and not prior to, this updated initiation date are included in reports from the main trial.