Wearable accelerometers are small, non-invasive devices that can be worn on the body to remotely collect detailed data on movement in free-living settings for multiple days at a time. They use microelectromechanical accelerometer sensors to measure gravitational acceleration (usually expressed in g-units) in one-to-three orthogonal axes with sampling frequencies between 10 to 100 observations per second.

As monitors can be worn continuously, without a need of removal at bedtime, they create new and exciting opportunities for multimodal assessment of physical activity, mobility, diurnal rhythms, and sleep. Moreover, wearable devices allow for fully remote data collection. Therefore, beyond the theoretical importance, this technology also has practical implications, given the inherent limitations to in-person healthcare for individuals in poor health or remote locations, which has become even more important during the COVID-19 pandemic.