Wireless Device Compatibility: Improving Patient Access to Cell Phone Technology

September 2011

Josara Wallber, AuD, CCC-A


Audiologists, whether dispensing hearing aids or not, must keep current with wireless technologies to best serve our patients. The term "wireless" is used to describe a number of connectivity options. In audiology, this includes speech and data transmission between hearing aids, hearing aid programming, and the coupling of hearing aids with such external technology and devices as FM, television, and cellular telephones (Sandrock & Schum, 2007; Yanz, 2009). This article focuses specifically on cellular telephone connectivity for hearing aid users.

Hearing Aids and Telephone Use

In December 2010, the number of cellular phone subscriptions in the United States exceeded 300 million: Cell phone penetration has reached 96%, compared with only 13% just 5 years earlier. In fact, more than 26% of all American households no longer have a landline telephone but depend solely on cellular phones (CTIA, n.d.). Meanwhile, more than 31 million Americans report experiencing hearing loss, and 1.4 million utilize hearing aids (Kochkin, 2005, 2009); certainly, these individuals are among the millions of cellular telephone subscribers.

Hearing aid users have historically experienced frustration in accessing telephone technology (Hall & Zakry, 1999). In fact, three quarters of those surveyed by Kochkin (2002) reported telephone use as unsatisfactory. Acoustic feedback was often the source of reported difficulty and was initially addressed by use of near-field magnetic induction (NFMI) coupling via hearing aid telecoils (Daigle & Stinson, 2002; Sanford, 2002). While hearing aid companies developed telecoils to capitalize on electromagnetic leakage from telephones, there was no requirement that the telecommunications industry make its devices compatible with hearing aids until 1988, when Congress passed the Hearing Aid Compatibility Act. This legislation required the Federal Communications Commission (FCC) to ensure that all "essential" telephones be compatible with hearing aids but specifically exempted cellular telephones. It did, however, allow the FCC to monitor the situation and revoke the exemption if necessary. Essential telephones were defined as coin-operated phones, telephones provided for emergency use, and others frequently needed by hearing aid users (FCC, 1988).

Since 1988, both the hearing aid and telecommunications industries have moved from analog to digital devices. While digital hearing aids have reduced problems with feedback, distortion, insufficient volume, and understanding in noise for telephone users through feedback cancellation, telephone programs, and noise management algorithms, there remains a significant number of users who still struggle with these problems (Recker & Kalluri, 2009). With the proliferation of cellular telephone use, the FCC withdrew the exemption for wireless telephones in 2003 and instituted a phase-in period for compliance.

Cellular Phone Coupling Methods

Today, hearing aids can be used on the telephone in one of four modes: acoustic, electromagnetically via a telecoil (either direct or indirect), direct input, or, in some high-end devices, via digital induction. In the acoustic mode, sound is transmitted via the microphone to the hearing aid, which has the disadvantages of picking up ambient room noise and being highly susceptible to acoustic feedback. In telecoil mode, the hearing aid microphone can be disabled, which has the advantage of reducing ambient noise and acoustic feedback. Telecoil strength is determined by the number of wire coils, which can be limited by size consideration in hearing aid designs. In fact, many smaller, custom products that fit in the ear may often have insufficient room to accommodate a telecoil (Compton, 1994). In addition, the orientation of the telecoil inside the instrument (horizontal vs. vertical) can affect the sensitivity of the coil to telephone handset inductive fields, which may be radial or axial (Barnes, 2009; Kozma-Spytek, 2010). Direct input is available on many devices via a direct input boot and cord that can be plugged into the cell phone. This does, however, tether the user to the phone. Digital induction is available in specific high-end hearing aid models and always requires the use of an auxiliary device that must be purchased from the hearing aid manufacturer. This arrangement (discussed further below) is subject to the least amount of interference and is not governed by FCC regulations. As hearing professionals, we need to assist our patients in navigating the maze of devices and coupling options. Indeed, Recker and Kalluri (2009) found that 56% of hearing aid users studied reported difficulty with coupling their aids to their telephone.

Direct Acoustic and Electromagnetic Coupling

Both hearing aid microphones and telecoils are subject to interference. In addition to the difficulties posed by orientation for proper reception, telecoils can pick up electromagnetic energy from sources other than telephones including electrical and electronic equipment (e.g., computer screens, fluorescent lights, and power lines). This means that while trying to use a cell phone via a telecoil, the hearing aid may also pick up interference from other parts of the phone, including the keyboard, circuit board, display, and battery (Victorian, 1998). Digital signal processing has been helpful in reducing, but not eliminating, this interference (Marshall, 2005).

Microphones are susceptible to interference from radio frequency (RF) emissions. RF is used primarily for communications that transfer information via radio wave energy. RFs are used to transmit information to and from the cellular phone and towers; therefore, the hearing aid may receive interference from the cellular phone antenna and/or transmitter.

Interestingly, as Class I medical devices, hearing aids are not regulated by the Food and Drug Administration (FDA) and are not subject to control concerning technical specifications or performance standards. For quality assurance purposes, hearing aids are subject to American National Standards Institute (ANSI) standards for performance measures. Conversely, telecommunications devices are subject to formal compatibility criteria under FCC regulation. There are also standards for telephones that define the performance criteria for compatibility. These include Electronics Industries Alliance (EIA) RS-504 for landline phones, ANSI/Telecommunications Industry Association (TIA) 1063 for cordless phones, and ANSI C63.19 for cellular phones. Known as the hearing aid compatibility (HAC) standard, it is this latter standard (IEEE/ANSI C63.19-2011) that we need to understand to assist our patients in making choices and in taking best advantage of cellular technologies.

Organization and Use of the HAC Standard

The standard is organized into two parts: one for microphone compatibility and one for telecoil compatibility. These are now simply referred to as M and T ratings, although they were originally labeled U and UT, respectively. Cellular telephones are rated from M1 to M4 (or U1–4), indicating the amount of RF interference they produce and therefore how well they will work with a hearing aid microphone. The T1–4 (or UT1–4) rating reflects the strength of electromagnetic induction available to a hearing aid's telecoil. Under the standard, a cellular phone is considered hearing aid compatible if it receives an M and/or T rating of 3 (ANSI C63.19). For a review of the methodology for determining these cell phone measures, see Seabury and Hill (2007). While the hearing aid industry is not mandated by the FCC to specific standards, the ANSI C63.19 HAC ratings apply only when a hearing aid is rated as an M2 and/or T2. This is a voluntary rating by the hearing aid industry that indicates the instrument's immunity to RF interference in the microphone mode (M rating) and/or its telecoil strength (T rating). Hearing aid manufacturers can add shielding to their instruments to make them less susceptible to RF interference when used in the microphone mode, and they may increase the power capability of their telecoils by making them larger (more coils). It is up to the end users to interpret these ratings to determine the probability that they will be successful in coupling their hearing aid with a cellular telephone. This is accomplished by adding the hearing aid rating (typically M2 and/or T2) to the cellular phone rating. Therefore, a hearing aid rated M2 (T2) plus a cellular phone rated M3 (T3) would produce a total rating of M5 (T5) and be considered acceptable for normal use. A sum of M6/T6 is considered excellent. Therefore, we should encourage our patients to purchase cellular phones with M4/T4 ratings whenever possible.

Access Aud Sept2011 figure

Figure 1. Symbol used to indicate a phone's HAC rating.

By law, phones that meet or exceed the M3 and/or T3 rating must display the information on the price placards in the cellular retail store, and these phones must be functioning for the customer to try in the store. The information must also be on the phone packaging; unfortunately, however, consumers rarely see the packaging until after the final sale. The standard highly recommends that retailers offer trial periods and return policies, but these are not mandatory. New benchmarks for wireless handset compliance were released in 2008 following negotiations between the telecommunications industry and the FCC. For the larger companies, this included the mandate that eight handsets (or 50% of the total, whichever was less) must be compatible. The number increased to nine in 2010. Again, these models must be available in the retail stores for consumers to try before they buy. There is no labeling requirement on the telephones themselves, but you can find the information at Phone Scoop. This site is a useful adjunct when working with patients in your offices.

Patients With Nonrated Cellular Devices

Cellular telephone companies utilize towers located across the country to transmit signals via RFs. There are three RF interfaces used in the United States: Code Division Multiple Access (CDMA), Integrated Digital Enhanced Network (iDEN), and Global System for Mobile Communications (GSM). There is some evidence that CDMA and IDEN cause less interference for hearing aid users than GSM (Kozma-Spytek & Harkins, 2005). Current users of each technology include the following: CDMA = Alltel, Sprint, U.S. Cellular, and Verizon; GSM = AT&T and T-Mobile; and iDEN = Nextel.

If a patient is considering an unrated phone, there are design factors that may influence a cellular phone's performance with a hearing aid. Phones that flip open, thereby increasing the distance between the hearing aid and RF transmitter, may reduce interference with hearing aid microphones. Smaller screen size and/or the ability to control the lighting of the screen can reduce interference with hearing aid telecoils (Kozma-Spytek & Harkins, 2005).

Bluetooth Technology

Bluetooth was invented by the Swedish company Ericsson, and in 1998 a group of companies formed the Bluetooth Special Interest Group (SIG). The SIG is an organization in which no one individual "owns" Bluetooth technology and all members work together to further develop and maintain the technology. The inventors wanted to use Bluetooth as a collaborative tool to connect multiple devices to share information quickly over the air. For example, computers could be connected wirelessly to a keyboard, mouse, or audio devices (Bluetooth SIG, 2011).

Bluetooth operates in an unlicensed industrial, scientific, and medical (ISM) band. The ISM band ranges from 2.4 to 2.485 GHz and is available in most countries. Bluetooth devices are connected through a pairing process in which a code, usually four digits, is shared between the two devices and a connection is created. The standards set forth by the SIG require a minimum range of 30 feet for Bluetooth devices; however, manufacturers are able to modify individual applications to improve overall range. Bluetooth performs well in interference because the signal "hops" up to 1,600 times per second to frequencies that are clear of interference. Bluetooth is widely used in computers and mobile devices for such information exchange as contacts, audio, pictures, and other applications. Bluetooth is able to simultaneously send and receive while a device is in use. Bluetooth devices can typically be paired with up to seven unique devices and is now commonly used in cellular telephones (Bluetooth SIG, 2011).

The terms "wireless" and "Bluetooth" are not the same, especially in relation to hearing aids. There are approximately 12,000 Bluetooth-capable devices on the market today; because Bluetooth is an open standard, it has been adapted for many purposes, including cell phones. Using Bluetooth directly within a hearing aid is currently impractical due to the amount of power required. An early adapter known as ELI was coupled to hearing aids via a direct auditory input boot or via the telecoil from an electromagnetic neck loop (Yanz, 2005). Today, when a hearing aid is defined as wireless, it is important to remember that this does not mean the hearing aid has Bluetooth; also, the type of wireless system on board hearing aids may differ from manufacturer to manufacturer. To use Bluetooth with hearing aids, a Bluetooth-capable adapter is needed to communicate with the source device, and this adapter must then transmit the signal to the hearing aids either through NFMI or RF signal (Groth, 2010).

Indirect Electromagnetic Bluetooth Coupling

All hearing aid users with telecoils have an easy option for coupling to Bluetooth devices. They may purchase a neck loop or silhouette with a Bluetooth receiver. In this way, the receiver can be paired with the cell phone, and an electromagnetic field is established in the neck loop or ear-level silhouette to transfer the information to the hearing aid. These devices are equipped with microphones, allowing the user hands-free operation of the telephone. Sample devices include the Artone neckloop, NoiZfree Beetle H-2ST, ClearSounds Quattro, and the CM-BT Audio Amplifier. Visit TecEar or Center For Hearing Loss Help for more information on these products.

Digital Induction Bluetooth Coupling

On-board RF technology is a newer method for transmission within hearing aids and is more expensive to implement because additional internal hardware is required. Internal RF allows for a set of hearing aids to communicate with each other for various options such as volume control changes, program changes, and focused listening. In addition, these digital wireless hearing aids are able to communicate with a remote control for these same features. In some cases, it is possible to connect with such Bluetooth devices as MP3 players, televisions, computers, and cell phones (Groth, 2010).

These hearing aids require an interface, specifically made by the manufacturer. Each hearing aid manufacturer employs its own proprietary device that must be purchased in addition to a hearing aid capable of working with the external device. Some examples include the Oticon Streamer, Phonak iCom, Siemens Teck, Sonic Innovations SonicBLU, and Resound Phone clip. These devices use Bluetooth to communicate with the user's phone and then RF to transmit the signal to the hearing aids (Groth, 2010). Currently, there are no standards or regulations governing these auxiliary aids.


As wireless technology evolves rapidly, persons with hearing impairment can benefit greatly from this technology. For hearing health care professionals, it is important to understand wireless connectivity and what this means for patients. For reviews of several current methods, see Campbell (2010), Diiulio (2011), and individual hearing aid manufacturer websites. Knowing what is available, we can guide patients to a solution that improves their ability to communicate and accomplish their individual hearing goals, particularly in accessing new and improving cellular telephone technologies.

Note on Cochlear Implants and Users of Sign Language

All currently available, FDA-approved cochlear implants (CIs) have internal telecoils, which means CI users can use cellular phones via direct acoustic and/or electromagnetic coupling. The latter may require special programming to activate and/or increase the signal from the telecoil over the microphone. Therefore, cellular phone M/T ratings should be considered for these patients. To date, however there is no M/T rating for the implants themselves, nor do any CI processors utilize digital induction. They all do, however, have direct input cords that can be plugged into a cell phone. Older models may or may not have telecoils; see individual manufacturers for additional information.

Deaf users of American Sign Language (ASL) were early adopters of cellular phone technology for text messaging. Texting, however, is devoid of the suprasegmental aspects of communication that convey subtle meaning, including emotions. For ASL users, this means losing facial and spatial markers, which is analogous to a hearing person's loss of voice intonation. The University of Washington has developed a cell phone application that allows sign language use over a cell phone (Lander, 2010). Because data transmission rates on U.S. cellular networks are currently about one tenth of those commonly used in Europe and Asia, this technology is not yet available here. Deaf subscribers are, however, already using this in Sweden and Japan. For a demonstration of this cellular phone technology, watch this YouTube video.

Portions of this article were previously presented at the Idaho State Speech, Language, Hearing Association annual convention. The author wishes to acknowledge AuD students Damon Boyce and Cory Workman for their work with wireless technology and contributions to the dissemination of this information.

About the Author

Josara Wallber, AuD, is an audiology clinical faculty member at Idaho State University (ISU), where she teaches aural rehabilitation and implantable technologies. Dr. Wallber supervises graduate students providing general audiology services and operates the ISU cochlear implant program in conjunction with East Idaho Ear Nose Throat. Contact her at


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