A Billion Smartphones, a Billion Potential Hearing Devices

There are more smartphones in the world than traditional hearing aids by several orders of magnitude. As of 2024, over 5 billion people own a smartphone. Of the 430 million people with disabling hearing loss, only a small fraction use any form of hearing assistance.

The mismatch has prompted a growing body of research into whether the device already in most people’s pockets can do something useful for their hearing.

The answer, according to peer-reviewed evidence, is nuanced: yes, with real limitations.

How Smartphone Hearing Aid Apps Work

At their core, hearing aid apps capture sound through the microphone, apply digital signal processing, and play the result through earphones — ideally in real time with minimal delay.

The critical variables are latency (delay between sound and output), gain accuracy (how well amplification matches the user’s hearing loss), and noise management.

Consumer smartphones have advanced to the point where real-time audio processing pipelines — including nonlinear gain, noise suppression, and acoustic feedback cancellation — can be implemented in software.

Petralex, one of the most-cited smartphone hearing aid apps in scientific literature, was developed by researchers at the Belarusian State University of Informatics and Radioelectronics and is backed by a US patent (US20160142538A1, 2016) and two Russian patents covering hearing compensation methods.

The Clinical Evidence: What Studies Show

The most directly relevant clinical evaluation of Petralex was published in the Journal of International Advanced Otology in 2022. Researchers at Seoul National University Hospital tested three hearing aid apps — EarMachine, Sound Amplifier, and Petralex — against a calibrated clinical hearing aid in seven participants with mild sensorineural hearing loss.

The key findings: clinical hearing aids produced the greatest gain, as expected. Among the three apps, Petralex was the only one to show a statistically meaningful improvement in word recognition score (6% improvement vs. unaided). EarMachine and Sound Amplifier showed limited benefit.

None of the apps improved signal-to-noise ratio in noisy conditions — a known limitation of smartphone hardware, which typically has a single microphone with no directional processing.

This finding is important to understand correctly: apps are not clinical hearing aids, and the gap is real. But for mild hearing loss, measurable benefit exists.

The Hearing Test: How Good Is It?

Most hearing aid apps include an in-built audiometric test to calibrate amplification to the user’s specific hearing profile.

The scientific literature on smartphone audiometry is mixed but increasingly positive. A 2022 study published in the American Journal of Audiology evaluated a smartphone-based hearing test (DuoTone) in 1,641 users and found test-retest reliability comparable to clinical audiometry for thresholds between 15 dB HL and 80 dB HL.

The evidence consensus: smartphone hearing tests are useful for screening and app configuration. They are not a substitute for clinical pure-tone audiometry in a soundproof room with calibrated equipment.

Live Listen and Remote Microphone Mode

One practical feature that makes smartphone hearing aids genuinely useful in specific situations is “live listen” — placing the phone near a sound source (a speaker, a TV, a person talking) and listening through earphones from a distance.

This replicates the function of FM listening systems used in classrooms and public venues.

A 2016 Springer paper cited Petralex specifically as an app enabling this function. A sample survey cited in associated research found that up to 70% of students with hearing impairment positively rated this type of app use in educational settings.

Who Benefits Most — and Who Should See a Doctor

Smartphone hearing aid apps are most likely to help people with mild to moderate sensorineural hearing loss who do not yet use any hearing assistance. They are not appropriate for people with severe or profound hearing loss.

Anyone who notices sudden hearing loss, asymmetric hearing loss, or hearing loss accompanied by dizziness, tinnitus, or ear pain should see a medical professional.

Smartphone apps are not diagnostic tools and cannot identify the cause of hearing loss.