<p>Digital cognitive behavioral therapy for insomnia (dCBT-I) has emerged as a treatment for chronic insomnia. Smart rings provide objective, wearable-derived sleep data that may complement subjective sleep diaries, but their role in monitoring treatment response remains unclear. This study evaluated the clinical effectiveness of dCBT-I with smart rings and compared subjective and wearable-derived sleep measures. In this single-arm study, individuals with insomnia completed a dCBT-I program, alongside daily sleep monitoring using a smart ring and sleep diary. Changes in clinical symptoms were analyzed, and sleep parameters were compared across the two tools. Twenty-eight participants completed the study<i>,</i> with significant improvements in insomnia severity (ΔISI = − 6.16,<i> p</i> = .011) and anxiety symptoms (ΔGAD-7 = − 2.38, <i>p</i> = .038). Adherence to the smart ring was higher than to sleep diaries (52.5 vs. 44.5&#xa0;days, <i>p</i> = .002). Sleep diaries showed significant improvements in sleep parameters, which were not reflected in smart ring data. Systematic differences were observed between data sources. dCBT-I combined with smart rings improved clinical symptoms. However, smart rings did not reflect sleep improvements seen in diaries, limiting their clinical use as a standalone monitoring tool for insomnia management.</p><p><i>Clinical trial registration</i> Study of Efficacy of Digital Cognitive BehavioralTherapy with Wearable Device for Insomnia. Registered on 24/03/2024, ClinicalTrials.gov (NCT06339853), <a href="https://clinicaltrials.gov/study/NCT06339853">https://clinicaltrials.gov/study/NCT06339853</a>.</p>