A miniature, low-cost IVR device using readily available electronic components, can provide accurate and quantitative determination of adherence to IVR-based HIV prevention methods. Adherence has been shown to be a primary factor in PrEP and microbicide clinical trial failures, and adherence monitoring may allow more accurate evaluation of product efficacy, identify factors influencing product use, and enable early interventions to ensure successful preventative therapy. Based on these initial in vitro and in vivo results, this adherence-monitoring IVR merits further development and evaluation in preclinical and clinical studies.