A CROS hearing aid is a specialized two-piece system designed for people who are deaf or have severe hearing loss in one ear but hear normally (or near-normally) in the other. Instead of trying to amplify sound in the impaired ear, the system picks up sound on that side and wirelessly sends it to the ear that can still hear. The name stands for Contralateral Routing of Signal.
How a CROS System Works
The system uses two devices that look like standard hearing aids. One sits on the impaired ear and acts purely as a microphone and transmitter. It captures sound arriving on your “dead” side and sends it wirelessly to a receiver worn on your better ear. That receiver plays the sound directly into the ear that can process it, so you hear voices and noises from both sides of your head through one functioning ear.
Most current CROS systems transmit the signal using near-field magnetic induction between the two devices, while also supporting 2.4 GHz wireless connections for streaming from phones and other accessories. Modern rechargeable versions can last up to 24 hours on a single charge, and many pair with smartphones via Bluetooth just like conventional hearing aids.
The Problem CROS Aids Solve
When one ear is completely deaf, your head itself blocks sound coming from that side. This is called the head shadow effect, and it’s most dramatic for higher-pitched sounds, which can lose 20 decibels or more by the time they travel around your skull to the good ear. Lower frequencies lose a smaller but still meaningful 3 to 6 dB. In practice, this means you can miss entire conversations happening to your impaired side, especially in noisy environments like restaurants or meetings.
CROS aids bypass this problem entirely by giving your good ear direct access to whatever the microphone on the impaired side picks up.
CROS vs. BiCROS
A standard CROS system is for people whose better ear hears normally. The receiver on that side doesn’t amplify anything; it simply plays the rerouted signal from the other side.
A BiCROS system is for people who have some hearing loss in their better ear too. The device on the better ear does double duty: it amplifies environmental sound for that ear while also receiving the transmitted signal from the impaired side. If your audiologist finds that your “good” ear also needs a boost, BiCROS is the version they’ll recommend.
Who Is a Candidate
CROS systems are designed for single-sided deafness, defined as severe to profound hearing loss in one ear with normal or near-normal hearing in the other. Common causes include sudden sensorineural hearing loss, acoustic neuroma surgery, infections, or trauma. There’s no strict minimum duration of deafness required, though many users have lived with single-sided deafness for a year or more before pursuing treatment.
People who still have some usable hearing in the impaired ear are usually better served by a conventional hearing aid on that side. CROS is specifically for situations where amplification in the bad ear won’t help because the hearing nerve or inner ear structures can’t process sound effectively.
What the Research Shows About Performance
CROS aids consistently improve speech understanding in noisy settings when the sound you’re trying to hear comes from your impaired side. A longitudinal study tracking CROS and BiCROS users found that speech perception in noise improved significantly after fitting, and performance kept getting better over the first six months of use. Listening effort, the mental energy required to follow conversation, also dropped as users wore the devices longer.
Research from multiple groups confirms these findings: when the target voice is directed toward the impaired ear, CROS users perform considerably better than they would unaided. The devices essentially eliminate the worst-case listening scenario for someone with single-sided deafness, where the speaker is on the deaf side and background noise is on the hearing side.
What CROS Aids Don’t Restore
The most important limitation is sound localization. Normal directional hearing depends on tiny differences in timing and volume between your two ears. Because a CROS system funnels everything into one ear, those binaural cues are lost. Research shows that CROS use can actually disrupt the localization strategies that single-sided deaf listeners develop on their own, including vertical localization at the open ear, which was “obliterated” in one study when the CROS device was turned on.
Users wearing CROS aids in localization tests showed slower reaction times, greater response variability, and reduced accuracy in identifying where sounds came from in both horizontal and vertical dimensions compared to unaided listening. The researchers noted that the device introduces a new, unfamiliar sound spectrum to the good ear that the brain may be able to relearn over time, but this adaptation isn’t guaranteed. In practical terms, you’ll hear sounds from your deaf side that you’d otherwise miss, but you may not always be able to tell which direction they came from.
Cost and Availability
A full CROS or BiCROS system includes both the transmitter and the receiver as a package. Retail pricing varies widely depending on the manufacturer and technology level. Signia’s current CROS-equipped models, for example, range from roughly $2,500 to $5,500 per pair at retail. State contract pricing (what Medicaid programs pay) runs much lower, from about $624 to $878 for a complete system across brands like Oticon, Phonak, Signia, ReSound, and Rexton.
Insurance coverage depends heavily on your plan. Some private insurers cover hearing aids with varying caps, while Medicare traditionally has not covered them. Medicaid programs in many states do cover CROS systems, often through negotiated volume-purchase contracts. It’s worth checking whether your state program or employer plan includes hearing aid benefits, since the gap between contract pricing and retail is substantial. Major manufacturers including Phonak, Oticon, Signia, ReSound, and Rexton all currently offer CROS-compatible models in both rechargeable and disposable-battery styles.