Hearables: Bioelectronics technological challenges and opportunities

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.

Keywords: biosignal; ear-EEG; hearable; wearable.

Figure 1.

Hearables represent a promising direction for wearable technology by leveraging the unique anatomical features of the ear, such as the concha and ear canal. These regions support discreet, comfortable, and stable sensor placement, enabling long-term physiological monitoring. The increasing research interest in ear-based wearables underscores their potential for personalized, low-power, and socially integrated health solutions.

Figure 2.

Various types of ear EEG electrodes have been developed in the field. (a) Generalized electrode design based on a common ear-hub (Kidmose et al., 2013). (b) Earhub-style electrode produced by molding (Sintotskiy and Hinrichs, 2020). (c) Earhub-style electrode with an integrated auricle holder (Looney et al., 2014). (d) Single-piece design combining the ear electrode and circuit board (Our ear-EEG) (L Yu et al., 2024). (e) 3D model of the integrated electrode and circuit board, featuring adjustable parameters including (outer diameter), (inner diameter), and (length), as well as customizable electrode shape and curvature. This design enables on-demand manufacturing tailored to individual anatomies across different age groups and genders. The rigid structure ensures a durable and reliable product suitable for everyday life, for example, if the device drops on the ground or is pressed a little bit while in the pocket, and so forth.

Figure 3.

ASSR test using (a) scalp EEG and (b) ear-EEG. Red lines indicate the timing of frequency changes, while green lines mark the expected auditory response frequencies (Yu et al., 2024).

Figure 4.

Comparison of ASSR test results between scalp EEG and ear-EEG across 20 subjects from the EESM19 dataset, where the signal-to-noise ratio (SNR) is defined as the power at 40 Hz relative to the average power in the 35–45 Hz band, excluding 40 Hz (Mikkelsen et al., 2019).

Figure 5.

Three major challenges affecting hearable device performance and signal quality: (a) Variability in ear anatomy, differences in ear canal shape and size among users result in inconsistent performance. (b) Motion artifacts, as hearables are designed for daily wear, while movement during activities introduces noise, reducing signal quality. (c) Size constraints, the limited space within the ear canal, restrict the number and size of components that can be integrated into the device.

Figure 6.

While current hearable technology often relies on microcontrollers and rigid-material electrodes produced through molding or partial 3D printing, leading to unstable signal quality, future advancements in both hardware and manufacturing techniques, such as the integration of neuromorphic chips with on-device AI and the use of flexible materials, promise more stable signal acquisition and real-time analysis. These innovations will greatly enhance and expand the applications of hearables across various domains.