Hearables were the largest wearable category in the world by shipment volume, with IDC forecasting hearable shipments to reach roughly 408 million units in 2026 — and a growing share of that volume is being driven by biometric health sensing rather than audio alone. What started as noise-cancelling earbuds and hearing aids is turning into a genuine health-sensing platform, sitting on a part of the body that turns out to have real physiological advantages over the wrist.
This post looks at why the ear is emerging as a serious location for physiological sensing, the engineering trade-offs that come with designing for it, and where the category still runs into real constraints.
Why the Ear, Physiologically
Sensor placement determines signal quality more than almost any other design decision in a wearable — a theme that comes up constantly in our own work on PPG-based sensing — see cuffless BP wearables and biosensor selection. The ear has two physiological properties that make it a genuinely strong candidate.
Blood flow near the ear is relatively stable and less affected by motion than at the wrist. The wrist is a mechanically noisy place to take an optical measurement — tendons, muscle movement, and variable sensor-to-skin pressure all introduce artifacts. The ear, particularly the concha and ear canal region, sits closer to the head with comparatively less soft-tissue movement during normal activity.
Published validation data backs this up. In a clinical study using a CE-marked in-ear PPG sensor evaluated against reference ECG across roughly 2,000 hours of recordings from 97 patients, the in-ear heart rate measurements showed a mean absolute percentage error of about 2.6%, with a correlation coefficient of 0.83 against the ECG reference. Separately, a 2025 research prototype comparing an earring-based PPG sensor to wrist- and ring-based alternatives found the ear-worn sensor's heart rate readings differed from a chest-strap reference by less than half a beat per minute on average — meaningfully tighter than the ring-based alternative in the same study, and notably more resistant to the motion artifacts that visibly degraded the wrist-worn comparison device during exercise.
- None of this means wrist-worn PPG is obsolete — it remains the more established, better-understood location. But the data is consistent enough that ear-worn sensing deserves to be treated as a legitimate primary sensing site, not just a secondary or novelty location.
From Hearing Aid to Health Monitor
The category shift is being driven by three converging trends:
Regulatory changes that lowered the barrier to hearing devices. The FDA's over-the-counter hearing aid rule opened the hearing aid category to a much broader consumer market, and manufacturers building for that category are increasingly layering health-sensing features on top of the same hardware.
Miniaturized sensors and low-power chipsets have matured enough to fit heart-rate PPG, accelerometry, and in some cases temperature sensing into an earbud-sized form factor without wrecking battery life.
Consumer demand for continuous, unobtrusive monitoring — the same demand pulling the broader wearables market toward rings and patches is pulling hearables in the same direction, with the added benefit that many people already wear earbuds for hours a day, meaning the "compliance" problem that limits data continuity in other wearable categories is much smaller here.
The result: hearing aids and premium earbuds are increasingly described as doubling as 24/7 health monitors, providing real-time insight across a wider range of users than fitness trackers historically reached, from older adults to athletes.
The Engineering Constraints That Are Unique to This Form Factor
Designing a health-sensing hearable isn't just "take a wrist PPG module and shrink it." The ear presents its own distinct set of constraints.
Extreme size and power budget. An earbud has dramatically less volume than a smartwatch case for battery, sensors, and compute — every additional sensor competes directly against battery life and comfort in a way that's more punishing than almost any other wearable form factor.
Fit variability across a huge range of ear anatomies. Unlike a wristband, which mostly needs to accommodate wrist circumference, an in-ear or on-ear device has to maintain consistent sensor-to-skin contact across widely varying ear canal and concha shapes — inconsistent fit directly degrades PPG signal quality, the same way loose wrist-strap tension does.
Thermal and acoustic co-design. Adding sensing hardware into a device whose primary job is still audio means the electronics, battery, and sensor placement all have to be negotiated against speaker and microphone placement, not just added alongside them.
Motion still matters, just differently. The ear is more stable than the wrist during arm movement, but head motion, jaw movement from talking or chewing, and the act of inserting/removing the device introduce their own artifact patterns that need dedicated signal-processing and IMU-based artifact rejection — not simply a copy of wrist-based motion-compensation algorithms.
Regulatory ambiguity at the edges. Ear-based sensors are gaining real traction for metrics like heart rate, temperature trends, and activity, but clinical-grade claims for more complex measurements still require the same kind of regulatory validation covered in FDA clearance for wearables — the hardware capability is arriving faster than the regulatory clarity around what claims can be made from it.
What a Health-Focused Hearable Architecture Looks Like
A hearable built for health sensing, not just audio, typically layers in:
- PPG sensor — optical heart-rate and, increasingly, SpO2 sensing, positioned to maintain consistent contact across ear shapes
- IMU — motion and orientation sensing, used both for activity context and for artifact rejection specific to head/jaw movement
- Temperature sensor — increasingly included for trend-level body temperature monitoring
- Low-power AFE and MCU — tuned aggressively for power, given the extreme volume constraints
- BLE radio — for offloading data to a phone or app, since heavy on-device storage isn't practical at this scale
- Edge inference — an increasingly common addition, since sending raw biosignal data over BLE continuously is a meaningful power cost of its own
This is very much the same multimodal-sensing philosophy we've covered in our posts on cuffless blood pressure monitoring and edge AI — the ear is simply a new, physiologically favorable location to apply it.
Conclusion
The ear turns out to be a genuinely strong location for physiological sensing — arguably a better one than the wrist for certain metrics, thanks to more stable local blood flow and lower susceptibility to motion artifact. What's holding the category back isn't sensing physics; it's the extreme mechanical, power, and fit constraints of building health-grade sensing into a form factor with almost no spare volume, plus a regulatory landscape that hasn't fully caught up to what the hardware can now measure.
At CoBuild Labs, we approach ear-worn and other novel sensor placements the same way we approach any wearable sensing challenge: starting from the physiology of the site, then working backward through AFE selection, mechanical fit, firmware, and validation to build a device that earns the accuracy claims it wants to make.
Designing an ear-worn or novel-placement wearable? Talk to CoBuild Labs — or read our wearable prototyping roadmap and electrical engineering approach.