Project Summary/Abstract We assess the feasibility of mobile technologies to study the psychophysiological underpinnings of affect in Opioid Use Disorder (OUD). In this feasibility pilot study, we will evaluate participants’ adherence to the procedures of a longitudinal study, including: 1. wearing wearable sensors for the duration of the study, 2. completing research activities involving prompted and self-initiated self-reports on momentary experiences of stress and negative affect. We will also examine the validity and reliability of the physiological data captured with two wearable sensors from two different brands and that are placed in different body locations. It is important to assess the reliability of data from two devices simultaneously to examine issues that may hinder a study’s viability, like data noise, signal problems, or data loss, etc. Lastly, we will utilize this data to investigate the role of autonomic function as a valid physiological marker of stress and negative affect in OUD. This has relevant implications in the understanding and development of digital treatments, as stress and negative affect are major contributors of relapse. This pilot work will contribute to the aim 2 of the parent grant by using digital and computational health cores to advance research in mHealth, artificial intelligence, and machine learning. In addition, the work supported under this supplement will serve as a building block to successfully create and submit an F31 grant proposal, a research that will be carried out following the diversity supplement period. This supplement will support the intensive training and invaluable practical experience that will advance the career of the trainee, Veronica Ramirez. This is in alignment with aim 6 of the parent grant to “expand the pipeline for early investigators” and create programs that support “addiction and substance misuse research, training, and mentorship”. Aligned with this, our research can ultimately help current efforts to address the opioid epidemic to ameliorate its detrimental effects on society.