ABSTRACT Nonadherence to medication therapy results in significant morbidity and mortality across the world. In the United States, medication nonadherence results in $528 billion of annual costs to healthcare to manage consequences associated with nonadherence including progression of chronic disease. For medication regimens like HIV pre-exposure prophylaxis (PrEP) and antiretroviral therapy (ART), morbidity associated with nonadherence includes acquisition and transmission of HIV, opportunistic infections, and exacerbation of chronic HIV related comorbidities. In order to understand adherence and mitigate nonadherence, new direct adherence tools that confirm ingestion events are needed. Current indirect measures detect surrogate indicators of adherence like self-report, pill counting, or electronic adherence devices that detect the opening of pill bottles. These methods suffer from recall bias and often provide an incomplete measure of adherence. In contrast, direct measures, such as directly observed or video observed therapy that utilizes a clinician or healthcare worker to visually confirm medication ingestion, can verify medication ingestion events. Yet, these direct methods are expensive, require personnel, and are therefore difficult to scale. Direct confirmation of drug concentration in serum or hair may be used as evidence of medication adherence, but these methods require specialized analysis techniques and provide overall adherence which may overlook periods of suboptimal adherence. In response to the limitations of both indirect and direct measures of adherence, digital pills—an ingestible radiofrequency emitter and gelatin capsule which over encapsulates the desired medication— represent a tool that can directly confirm medication ingestions and innovatively provide feedback to both the user and care team. In 2019, etectRx received FDA 510K clearance for the ID-Cap, a digital pill system that directly measures medication adherence in real-time. Through K23DA044874 and independent investigator- initiated research grants from Gilead Sciences, we have demonstrated the feasibility of using the ID-Cap System among individuals to measure adherence to PrEP and opioids. During these investigations, we discovered widespread interest among patients in optimizing the system by developing a wrist-borne wearable Reader to collection adherence information from the digital pill. This Phase I SBIR therefore develops the next- generation ID-Cap System with a wrist-borne wearable reader. In Aim 1, we will miniaturize the current version of the Reader and conduct laboratory testing to ensure all components are functional and acquire signal from ingested digital pills. Next, in Aim 2, we will conduct an open-label pilot demonstration trial to understand the real-world usability of the next generation ID-Cap System among N=30 individuals on PrEP (N=15) and ART (N=15). Our benchmarks for success, the development of a miniaturized wrist-worn reader and de...