Is my smartwatch a valid witness? A systematic review and meta-analysis

Wearable devices are being increasingly used not only in traditional research fields (e.g. clinical, health) but also in innovative ones such as digital forensics. Modern commercial smartwatches, equipped with sensors like accelerometers, gyroscopes, and photoplethysmographs, can record activity, heart rate, sleep, and other physiological parameters that may support forensic investigations, given that their data is valid. To perform a first step in studying such validity, this article presents a systematic review and meta-analysis summarizing the available studies validating data collected from smartwatches, focusing on their potential use in forensic investigations. The review examined studies evaluating smartwatches from four major brands, comparing their outputs, such as activity classification, step count, distance, heart rate, energy expenditure, and sleep metrics, against established gold-standard measures. We found that not all brands of smartwatches and not all outcomes were equally studied, with varying results in terms of accuracy, protocols, and reporting of results. Heart rate resulted the most studied (and most accurate) measure. Most studies validated smartwatches in healthy populations and performed validation in laboratory settings. Overall, while smartwatches show promise for enhancing digital forensic analyses, their current validation evidence is heterogeneous. The findings highlight the need for more extensive and standardized validation efforts, larger and more diverse study populations, and improved transparency from manufacturers. These conclusions are not only relevant for forensic applications but also extend to broader domains, such as clinical and health research, where the reliability of wearable-derived data is equally critical.