A CROS hearing aid is a two-part system designed for people who have little or no usable hearing in one ear. Instead of trying to amplify sound in the deaf ear, it picks up sound on that side and wirelessly routes it to the ear that can still hear. The name stands for Contralateral Routing of Signal, and it’s one of the primary treatment options for single-sided deafness.
How CROS Hearing Aids Work
The system uses two devices that look like standard behind-the-ear hearing aids, one worn on each ear. The device on your deaf or non-functional ear contains microphones and a processing chip but no speaker. It acts purely as a transmitter, capturing sounds from that side of your head and sending them wirelessly to the receiving device on your better ear. That receiver plays back the transmitted audio so you can hear what’s happening on your deaf side.
This wireless transmission originally relied on radio frequency technology dating back to the 1970s. Modern systems use far more sophisticated digital wireless protocols that deliver clearer, faster audio with less delay. The result is a more natural listening experience, though you’re still hearing everything through one ear.
CROS vs. BiCROS Systems
The choice between CROS and BiCROS depends on how well your better ear hears. A standard CROS system is for people whose better ear has normal hearing. The receiver on that side simply plays the transmitted sound without adding any amplification of its own.
A BiCROS system is for people who have hearing loss in both ears, but one ear is so impaired that it can’t benefit from a hearing aid at all. In this case, the receiver on the better ear does double duty: it picks up and amplifies sounds on its own side (like a traditional hearing aid) while also receiving the transmitted signal from the worse ear. Both microphones feed into a single ear, giving you coverage from both directions with amplification tailored to your remaining hearing.
Who Needs a CROS System
CROS devices are designed for people with single-sided deafness, defined as moderate-to-profound hearing loss with limited speech perception in one ear and normal (or near-normal) hearing in the other. Several conditions can cause this kind of asymmetric loss:
- Acoustic neuroma: a benign tumor on the hearing nerve that can destroy hearing on one side, sometimes as a result of surgical removal
- Sudden sensorineural hearing loss: an unexplained, rapid loss of hearing in one ear that doesn’t recover
- Chronic ear disease or infections: long-term damage that makes one ear unaidable
- Congenital single-sided deafness: being born without functional hearing in one ear
The key criterion is that the poorer ear can’t benefit from a conventional hearing aid. If amplification could help both ears, a standard pair of hearing aids would typically be the better option. CROS technology fills the gap when one ear is essentially beyond help.
The Head Shadow Problem
Your head is a physical barrier to sound. When someone speaks on your deaf side, the sound has to travel around your skull to reach your good ear, losing volume and clarity along the way. This is called the head shadow effect, and it’s one of the biggest daily frustrations of single-sided deafness. You might miss half a conversation at a dinner table, struggle in meetings, or constantly need to position yourself so your good ear faces the speaker.
CROS devices directly address this by capturing sound on the blocked side and delivering it to your hearing ear. Research consistently shows meaningful improvement: one study found a 32% improvement in speech recognition in noisy environments when using a CROS device. Scores jumped from about 30% correct without the device to nearly 63% correct with it. Across the broader research literature, improvements typically range from about 13% to 33% in speech recognition, or 4 to 10 decibels of effective benefit in noise. That’s a substantial difference in real-world situations like restaurants, classrooms, and open-plan offices.
What CROS Devices Can’t Do
Because all sound is ultimately delivered to a single ear, CROS hearing aids do not restore true two-eared hearing. The most significant limitation is sound localization. Your brain determines where a sound is coming from by comparing the tiny differences in timing and volume between your two ears. When both sides feed into the same ear, those cues disappear. You’ll hear more of what’s happening around you, but you still won’t be able to pinpoint direction reliably.
CROS systems also don’t help in situations where noise is coming from the good-ear side and the signal you want is on the deaf side. In that scenario, the device can actually route more noise into your hearing ear along with the desired sound. Some modern systems use directional microphones and noise-reduction algorithms to minimize this, but it remains a real-world trade-off.
Battery Life Considerations
The transmitter on your deaf ear works harder than the receiver because broadcasting a wireless signal continuously draws more power than receiving one. This means the transmitter’s battery drains faster than the receiver’s. If you notice one side dying well before the other, it’s almost certainly the transmitter. Planning for slightly more frequent battery changes or charges on that side is normal. Rechargeable models have become standard in recent years, which simplifies the routine, though you may still notice uneven drain between the two devices.
Cost of CROS Hearing Aids
CROS systems are priced as a pair since you need both the transmitter and receiver. Entry-level systems typically run $2,200 to $3,500, while premium models with advanced noise management and connectivity features range from $4,000 to $6,500. BiCROS systems, which add amplification on the better ear, tend to fall between $3,500 and $6,000. Warehouse retailers like Costco offer CROS options in the $1,400 to $2,800 range.
These prices generally include the professional fitting, follow-up adjustments, and a two- to three-year manufacturer warranty covering repairs and loss replacement. Insurance coverage varies widely. Some plans cover hearing aids partially or fully, while others exclude them entirely. It’s worth checking whether your plan distinguishes between standard hearing aids and CROS systems, as coverage policies sometimes differ.
Alternatives to CROS Devices
CROS hearing aids aren’t the only option for single-sided deafness. Bone-conduction devices transmit sound through the skull bone to the inner ear on the hearing side, achieving a similar rerouting effect. Some are worn on a headband, while others require a minor surgical procedure to anchor a small implant behind the ear. For candidates who qualify, a cochlear implant on the deaf side can restore some degree of actual hearing to that ear, potentially improving sound localization in ways a CROS system cannot. Each approach has different trade-offs in terms of invasiveness, cost, and the type of hearing it provides. An audiologist can help determine which option best fits your specific hearing profile and lifestyle.