Abstract
Wearable devices placed in or around the ear, often referred to as hearables, are gaining attention as alternative tools for pseudo-continuous health monitoring. Among their several capabilities, hearables are primarily useful for monitoring brain activity electronically via electroencephalography (EEG), enabling noninvasive, long-term recording of neural signals (e.g., from the ear canal). In addition to EEG, hearables can monitor heart rate, oxygen saturation, and temperature, all while maintaining the comfort and discretion of everyday items like earplugs or headphones. This review explores recent progress in combining multiple sensors, leveraging artificial intelligence (AI), and developing novel materials that make hearables more accurate, practical, and comfortable. On-device AI enables real-time, personalized insights that can support therapeutic interventions for neurological disorders like epilepsy. We seek further improvements in design and materials beyond this proof-of-concept, including three-dimensional printing with flexible electrodes while maintaining the unique property of monolithic circuit integration during system printing. That helps devices conform even better to the ear's anatomy for enhanced comfort and signal quality, while the rigidity of the main structure ensures a highly durable and reliable product suitable for everyday life. In particular, personalization through additive manufacturing enables custom-fitted hearables based on each user's unique ear canal features, supporting long-term wearability and reliable EEG acquisition. This review also addresses key challenges like motion artifacts and miniaturization, and current strategies to overcome them. Overall, this review highlights hearables as a key emerging technology, especially for EEG-based brain monitoring, offering a personalized, continuous, and noninvasive approach to future healthcare.