Is HAC mandatory for all phones sold in the United States?

Yes, since the universal mandate took effect on 3 April 2024. The FCC, through its Report and Order FCC 22-86 of 14 December 2022, extended the HAC obligation to 100 percent of mobile phone models offered under a US licence, whereas the previous regime relied on a progressive quota (50 percent then 66 percent of the portfolio). Every handset, including smartphones, VoLTE cordless fixed phones, two-way satellite phones and voice-interface IoT terminals falling within the scope of 47 CFR 20.19, must now show an M3 or higher rating and a T3 or higher rating to be placed on the market.

What is the difference between the M rating and the T rating?

The M rating (microphone, or acoustic-coupling) characterises the air-path coupling between the phone speaker and the hearing aid microphone. It reflects the level of radiofrequency interference generated by the phone in the vicinity of the hearing aid microphone, measured in V/m at the carrier frequency. The T rating (telecoil, or tele-coil-coupling) characterises the magnetic coupling between the phone audio-frequency coil and the telecoil built into the hearing aid, measured in dB(A/m) within the audio band. A HAC phone must satisfy both requirements simultaneously, with a separate threshold for each path.

What does the 2019 version of ANSI C63.19 change compared with 2014?

ANSI C63.19-2019 explicitly extends the procedure to sub-6 GHz 5G NR bands and to Wi-Fi on 5 GHz, whereas the 2014 version in practice covered only up to LTE and Wi-Fi 2.4/5 GHz. The 2019 version also clarifies the frequency scan procedure on wideband channels, the handling of beamforming antennas, and the evaluation of phones with hands-free loudspeakers. The FCC, in KDB 285076, published a transitional matrix accepting C63.19-2014 reports up to a cut-off date before full switchover to 2019. New submissions since 2023 almost all rely on the 2019 edition.

Does HAC apply to Wi-Fi-only devices or to voice-interface IoT?

The FCC extended scope in stages. The universal mandate of April 2024 covers cellular mobile phones. Wi-Fi-only terminals offering a service-level telephony function (VoWiFi, hardened VoIP apps supplied by an operator) also fall within scope under amended 47 CFR 20.19. Occasional voice-interface IoT devices (voice command of a thermostat, for example) remain outside the HAC scope as long as they do not offer a two-way real-time telephony service. Vehicles with on-board emergency calling (eCall, vehicle-integrated phone) benefit from partial exclusions defined in 47 CFR 20.19(b).

Is HAC required outside the United States?

Not through a direct equivalent federal mandate. The European Union has no general regulatory obligation for HAC rating of mobile phones: the RED 2014/53/EU directive addresses EMC via article 3.1(b) and health via article 3.1(a), without a hearing-aid-specific threshold. A few jurisdictions, such as Australia via AS/CA S040 and Canada via SP-Std-503, define references close to the US model. Most global manufacturers nonetheless align design with the FCC threshold to avoid a dedicated hardware variant for the US market.

Is a SAR-compliant product automatically HAC-compliant?

No. SAR (47 CFR 2.1093) characterises radiofrequency power absorbed by biological tissue, while HAC (47 CFR 20.19) characterises the interference of the phone near field with hearing aid components. The thresholds, the phantoms, the bands evaluated and the measured quantities differ. A phone may show a comfortable SAR yet fail M3 if the antenna radiates strongly in the near zone of the hearing aid microphone, or conversely pass HAC but struggle with SAR if the local peak power is too concentrated. The two campaigns are planned together to share the bench and the schedule, but the reports remain separate.

How does HAC testing articulate with ANSI C63.20 for wireless headsets?

ANSI C63.19 addresses HAC for telephony handsets. ANSI C63.20 addresses HAC for wireless headsets (Bluetooth primarily) and other wireless audio accessories that interact with a hearing aid. The methods derive from C63.19 but introduce configurations specific to in-ear earbuds and circumaural headphones. A product that combines handset and headset (smartphone shipped with Bluetooth earbuds) may fall under both standards. The FCC does not formally mandate C63.20 in 47 CFR 20.19, but TCBs often require it to close the file of a product with Bluetooth accessories.

What are the most common mistakes in HAC preparation?

Four mistakes recur. First, discovering the HAC requirement at the pre-submission FCC stage and having to redo a full measurement cycle: the requirement must be recorded in the product specification from concept stage. Second, omitting the T-coil evaluation and focusing on the M rating only: since 2024 the universal mandate requires both. Third, confusing SAR compliance with HAC compliance, assuming that a single report covers both: two campaigns and two sets of measurements are needed. Fourth, underestimating equipment: HAC requires specific audio probes (B and K or equivalent), a certified quiet audio room, and instrumentation able to isolate the near field, equipment not found in every general-purpose EMC laboratory.

HAC: Hearing Aid Compatibility (FCC 20.19, C63.19)

Author Hugues Orgitello Last updated 27 May 2026 ~15 min read

FCC regulatory guide, US requirement

Hearing Aid Compatibility, or HAC, is the US requirement that obliges every mobile phone placed on the US market to demonstrate an acceptable level of radiofrequency interference and magnetic-field coupling with hearing aids worn by users. The framework is set by the FCC in 47 CFR 20.19, the measurement method by ANSI C63.19, and the scope expanded in April 2024 through a universal mandate requiring that 100 percent of models sold be rated M3 or higher and T3 or higher. This page covers the regulatory genesis from the Hearing Aid Compatibility Act of 1988 and its 2007 modernisation, the ANSI C63.19 metrology, the M and T numerical thresholds, the 2024 universal mandate, the distinction with SAR, and the most frequent pitfalls when preparing an FCC file for a product with a voice interface.

Regulatory genesis: from HAA 1988 to the 2024 universal mandate

The HAC requirement rests on a legislative and regulatory stack that every product manager must understand to anticipate evolution.

Section 710 of the Communications Act of 1934

The legal basis goes back to the Communications Act of 1934, codified in 47 USC. Section 710, added by the Hearing Aid Compatibility Act (HAA) of 1988 (Public Law 100-394), requires that all telephones manufactured or imported for use in the United States after August 1989 be compatible with hearing aids. The HAA then targeted wired telephones, in a context where T-coil coupling was the near-exclusive amplification path for hearing aid users.

2003-2007 modernisation for mobile

The FCC, through its 2003 Report and Order (FCC 03-168), extended the requirement to mobile phones, recognising that the historical exclusion of wireless handsets in the original HAA could no longer be justified in the era of widespread mobile use. The FCC defined the M3 and M4 ratings for acoustic coupling, T3 and T4 for T-coil coupling, and imposed a progressive quota on operators and manufacturers: a given percentage of the portfolio had to be HAC. The successive amendments of 2007, 2008 and 2010 raised the portfolio threshold, integrated new bands (AWS, 700 MHz), and formalised quarterly and annual reporting.

2022 universal mandate, effective April 2024

The Report and Order FCC 22-86 of 14 December 2022 carried out the major shift. The FCC found that M and T coupling technologies were mature and widely deployed, that the per-model cost increment had become marginal, and that the historical quota left coverage gaps penalising hearing-impaired users. The universal mandate therefore requires that 100 percent of mobile phone models offered to the US public under an FCC licence be HAC, with M3 or higher and T3 or higher rating, with effective date 3 April 2024 for models submitted for authorization and certification from that date. The FCC transition table allows a grace period for models already in authorization before the cut-off date, but every new submission since April 2024 must tick the dual M and T requirement.

Timeline

Year	Regulatory act	Scope
1934	Communications Act	General framework for US telecommunications
1988	HAA, Public Law 100-394	Section 710 added, HAC for wired phones
2003	FCC Report and Order 03-168	Extension of HAC to mobile phones
2007	FCC 07-187, 08-68 (in 2008)	M and T ratings, portfolio quotas
2010	FCC 10-167	Integration of new services and bands
2017	FCC 17-94	Removal of the dual rating loophole, addition of VoLTE
2022	FCC 22-86	100 percent universal mandate, effective 2024
2024	3 April 2024	Effective date of the universal mandate

Structure of 47 CFR 20.19

The regulatory core fits within a specific paragraph of title 47 of the Code of Federal Regulations.

47 CFR 20.19(a), definitions and scope

Subparagraph (a) defines the terms: "hearing aid-compatible", "M rating", "T rating", "wireless handset", and bounds the scope. The scope covers "wireless handsets" understood as devices offering an interactive voice service on CMRS (Commercial Mobile Radio Service) services, which includes cellular phones, VoLTE phones, operator-subscription VoWiFi terminals, and certain two-way voice-interface IoT terminals.

47 CFR 20.19(b), technical requirements

Subparagraph (b) refers to ANSI C63.19 for measurement methodology, fixes the M3, M4, T3, T4 thresholds, and details the conditions for declaration and labelling. The April 2024 universal mandate was inscribed in (b). The section also specifies partial exclusions, notably for certain vehicle-embedded phones dedicated solely to emergency calls (eCall), for which the FCC allows a derogation conditioned by technical documentation.

47 CFR 20.19(c) through (f), declaration and labelling regime

The following subparagraphs frame the regime of public declaration and periodic reporting to the FCC. The manufacturer must publish the M and T rating on the product sheet, the operator must display HAC availability in-store and online, and an annual aggregated report in CSV or PDF format is submitted to the FCC. Failure to comply with the declaration regime is a separate infringement from failure to meet the technical rating, and gives rise to financial penalties framed by 47 CFR 1.80.

See The FCC for the general framework of the US certification regime and FCC tests for the test chain required for a complete submission.

The ANSI C63.19 method

The ANSI C63.19 standard, drafted by the Accredited Standards Committee C63 of the IEEE, is the sole metrological reference cited in 47 CFR 20.19.

History and versions

Three versions coexist in current practice:

ANSI C63.19-2007: historical version, coverage of GSM, CDMA, first 3G bands. No longer accepted for new submissions.
ANSI C63.19-2014: extension to LTE and first Wi-Fi bands. Still accepted transitionally under KDB 285076 up to a cut-off date, but to be avoided for any new submission after 2023.
ANSI C63.19-2019: current version. Covers sub-6 GHz 5G NR bands, 5 GHz and 6 GHz Wi-Fi, and formalises scan procedures for beamforming configurations. De facto reference for any FCC HAC submission since 2023.

The FCC, in KDB 285076, publishes a transition matrix explaining which version of C63.19 is required according to the submission date, the embedded radio technology, and the target rating.

Test bench and fixtures

A HAC campaign takes place in a laboratory equipped for near-field measurement in a controlled audio environment. Three elements characterise the bench:

A semi-anechoic chamber or a certified quiet audio area, with residual background noise typically below 25 dB(A) to avoid polluting the T-coil coupling measurement.
A handset positioning device in the Articulation Pole Position zone defined by the standard, that is, the position of a handset held to the ear in conversation. The fixture is typically a dummy head with a reference microphone and a magnetic-field sensor inserted in the zone corresponding to an ear canal fitted with a hearing aid.
An audio magnetic-field sensor (typically a calibrated coil of the Bruel and Kjaer type or equivalent) and an RF electric-field probe for the M path, calibrated to the frequency and band being evaluated.

M path: RF interference at the hearing aid microphone

The M path evaluates the radiofrequency electric field radiated by the phone in the near zone of the microphone of an in-the-ear or behind-the-ear hearing aid. The measurement is taken with the handset placed in worst case (maximum power, antenna configured as in real use) and the E field recorded in V/m at the microphone position simulated in the fixture, on the operational bands of the handset. The rating is determined by the combination of the V/m value and the modulation category (RF noise category) of the signal, according to the tables of ANSI C63.19. The higher the M rating, the less RF interference the handset generates near the hearing aid.

T path: magnetic coupling with the T coil

The T path evaluates the magnetic coupling between the audio-frequency coil of the handset (typically a speaker drive or a dedicated coil in high-end phones) and the T coil (telecoil) built into most hearing aids. The measurement is taken in the audio band (300 Hz to 3.3 kHz typically), with a calibrated magnetic probe positioned in the zone corresponding to the T coil of the hearing aid. The rating depends on the useful audio magnetic field strength (conversation signal) and the absence of stray magnetic noise in the same band. The higher the T rating, the more efficient the coupling for the end user.

M3, M4, T3, T4 ratings: threshold table

The heart of HAC compliance lies in four ratings whose thresholds are published in ANSI C63.19 and repeated in 47 CFR 20.19.

Rating	Path	Quantity evaluated	ANSI C63.19 threshold	Practical reading
M3	Acoustic (RF at microphone)	RF E field in near zone	Acceptable level, category 3	Minimum required since 2024
M4	Acoustic (RF at microphone)	RF E field in near zone	Stricter level, category 4	Recommended for premium
T3	T-coil (magnetic field)	Useful audio strength vs noise	Acceptable level, category 3	Minimum required since 2024
T4	T-coil (magnetic field)	Useful audio strength vs noise	Stricter level, category 4	Recommended for premium

The precise numerical thresholds (V/m for M, dB(A/m) for T, and signal-to-noise quality coefficients for both paths) are listed in tables 1 to 4 of ANSI C63.19-2019. The standard is under IEEE copyright and requires purchase for access to the exact figures. The reader should take the levels expressed here in words as reflecting the structure of the tables without reproducing their values: any measurement report must cite the thresholds of the exact C63.19 version used.

Why M4/T4 rather than M3/T3

The universal mandate requires M3 and T3 minimum. Several manufacturers nonetheless aim for M4 and T4 for two reasons. The first is marketing: a phone rated M4/T4 is perceived as premium by hearing-impaired users and their prescribing ENT specialists. The second is defensive: the extra margin absorbs manufacturing drift and last-minute adjustments (antenna change, band addition), avoiding a return to the laboratory at pre-production stage.

HAC vs SAR: two separate requirements

The HAC / SAR confusion is the most common cause of planning errors in product preparation. The two requirements coexist in an FCC file for a phone, but they cover different physical quantities and health objectives.

Criterion	SAR (47 CFR 2.1093)	HAC (47 CFR 20.19)
Health objective	Limit RF absorption by tissue	Ensure phone usage with a hearing aid
Measured quantity	SAR in W/kg, 1 g average	RF E field in V/m and magnetic field in dB(A/m)
Phantom	SAM head or flat body phantom	Dummy head with built-in T coil
Measurement band	100 kHz to 6 GHz (carrier), plus mmWave in density	Cellular carrier + audio band (300 Hz to 3.3 kHz)
Methodological standard	IEC 62209 (transposed EN)	ANSI C63.19
Validation limit	1.6 W/kg over 1 g (US)	M3+, T3+ minimum since 2024
Coupling type studied	Volumetric absorption in tissue	RF interference + audio magnetic coupling

For SAR context, see SAR procedures (IEC 62209, EN 50360). For the terminology definitions used here, see the Glossary.

Concrete case: a product can be SAR-OK and HAC-KO

A smartphone with its main antenna housed at the top of the device, optimised for an acceptable 1 g averaged SAR, can nonetheless generate high field density in the immediate vicinity of the earpiece speaker, the exact zone of the HAC M-path fixture. Conversely, a very RF-economical phone (and therefore HAC-friendly) may show a SAR limited by poor spatial distribution of the field in the phantom. The two campaigns are therefore independent in practice, even if they are scheduled over the same period to share the bench and the instrumentation.

Geographic coverage: is HAC required outside the USA?

HAC is primarily a US topic. The regulatory map is uneven.

Region	Equivalent HAC requirement	Reference
United States	Mandatory, universal mandate	47 CFR 20.19 + ANSI C63.19
European Union	No direct requirement	RED 2014/53/EU article 3.1(a) health, 3.1(b) EMC, with no dedicated HAC threshold
Canada	Recommended / aligned with FCC	ISED SP-Std-503, derived from ANSI C63.19
Australia	Dedicated reference	AS/CA S040, requirements close to the FCC model
United Kingdom	No direct requirement post-Brexit	UK PSTI framework and UK Radio Equipment Regulations with no dedicated HAC
Japan	Indirect reference via MIC	No universal mandate
South Korea	Indirect reference via KCC	No universal mandate
Brazil	No specific ANATEL requirement	May follow global manufacturer practice

For a global manufacturer, the common practice is to design the US version HAC-compliant and to deploy it worldwide, thereby avoiding hardware fragmentation. See The RED for the general European framework and RED tests for radio, health and EMC testing.

Special cases and exclusions

47 CFR 20.19(b) and the associated KDBs describe several special cases and partial exclusions.

WLAN-only and VoWiFi devices

Phones offering a voice service only over Wi-Fi (operator-subscription VoWiFi, voice applications integrated into the service of an MVNO) were brought into the HAC scope in 2017 by FCC 17-94. A pure Wi-Fi terminal without an associated CMRS function remains out of scope as long as it does not offer a two-way service-quality telephony service. The boundary is not always clear-cut, and the FCC rules case by case through KDBs and ruling letters.

Vehicle-embedded phones (eCall, ambient calling)

Cellular phones integrated into a vehicle, dedicated to emergency calls (eCall for the EU, functional equivalent for the US market) or to user comfort (automotive Wi-Fi hotspot with voice function), benefit from partial exclusions. The derogation is grounded in the fact that the device is not held to the ear in normal use but used via the vehicle audio system. Technical documentation must demonstrate the usage mode and the absence of an associated portable handset.

Two-way satellite phones

Satellite phones (Iridium, Inmarsat, AST SpaceMobile, Starlink direct-to-cell services emerging in 2024-2025) fall within the HAC scope since the FCC clarified in 2023 that mobile satellite telephony services supplied under US licence are CMRS within the meaning of 47 CFR 20.19. The first HAC submissions for direct satellite terminals appear in the FCC catalogue in late 2024.

Articulation with ANSI C63.20 (wireless headsets)

ANSI C63.20-2019, published in parallel with C63.19-2019, addresses HAC for wireless audio accessories (Bluetooth headsets, in-ear earbuds, circumaural headphones), that is, devices that interact acoustically or magnetically with a hearing aid without constituting a telephony handset in the strict sense.

For a smartphone shipped with branded Bluetooth earbuds (which has become standard since 2020), the FCC TCB typically requests:

An ANSI C63.19 campaign for the handset (smartphone).
An ANSI C63.20 campaign for the audio accessories shipped in the catalogue.
A joint declaration in the product file.

ANSI C63.20 is not formally mandated by 47 CFR 20.19, but TCB practice is to require it to close a complete file for a product with Bluetooth accessories. For accessories not shipped in a bundle (purchased separately), HAC responsibility falls back on the accessory manufacturer alone.

Real-Ear Measurement and volume control

Two complementary functional requirements were added to the HAC regime through successive amendments.

Volume control consistent with HAC

47 CFR 20.19 requires that the handset volume-control range allow a hearing aid user to obtain a comfortable audio level without saturating or going below the audibility threshold. The specification is qualitative in the regulatory text, but ANSI C63.19 sets a minimum regulation range and an acceptable linearity. A handset that does not offer a sufficient volume range may be HAC-compliant on the M and T paths but non-compliant on the volume-control path, which invalidates the file.

Real-Ear Measurement (REM)

Real-Ear Measurement is the audiological reference technique used by ENT specialists to verify the actual adequacy of hearing-aid amplification to the wearer's ear canal. Although REM itself is not a regulatory obligation imposed on the phone manufacturer, ANSI C63.19 cites REM as the physiological reference of the evaluation zone: the HAC fixture is designed to reproduce the conditions under which an audiologist would verify the hearing aid in REM. Metrological traceability of the HAC result back to REM is considered a strength of the product file, without being mandatory.

Classic pitfalls in HAC preparation

First-pass rejections at TCB on the HAC part come from four recurring causes.

Late discovery of the HAC requirement. The product team sets the specification without explicitly including HAC, assuming it is covered by SAR or by general EMC. The laboratory discovers the requirement at pre-submission stage, and a second campaign must be ordered (two weeks, 8,000 to 15,000 EUR) with possibly an antenna re-spin if the target rating is not reached. The rule is to record HAC M3+ T3+ in the specification from concept stage and to open a dedicated budget for the HAC laboratory.
Omission of the T-coil path. Before the April 2024 universal mandate, many manufacturers settled for an M rating without implementing a dedicated audio T coil. Since 2024, the dual rating is mandatory. A product that has not planned a specific drive circuit for the T coil at the electronic design stage ends up having to add a component at a late phase, which impacts the BOM, PCB routing and enclosure. The rule is to include the T-coil drive in the initial schematic for US-targeted phones.
Confusion between SAR compliance and HAC compliance. The certification lead assumes that the SAR report covers the HAC requirement. This is never the case: these are two separate campaigns, two reports, two sets of instrumentation. The rule is to schedule two parallel campaigns at the same laboratory if possible, sharing the bench but with two sets of fixtures and two sets of probes. For an overview of the associated FCC tests, see FCC tests.
Wrong product classification. A voice-interface IoT terminal (for example a smart speaker capable of placing a phone call via VoIP integrated into an operator service) can fall within the HAC scope without the product team anticipating it. The rule is to verify the CMRS classification of the product with an FCC consultant or directly with a TCB at concept stage, before design freeze.

See FCC pitfalls for the general pitfalls of a US certification file and FCC procedure for the full submission chain.

Schedule and cost of a HAC campaign

For a go-to-market budget, here are the orders of magnitude observed in an ISO/IEC 17025 accredited laboratory recognised by the FCC for HAC testing.

Product type	Configurations to evaluate	Campaign duration	Indicative cost
Single-band LTE mobile phone	8 to 15	4 to 6 days	6,000 to 10,000 EUR
Multi-band 4G + sub-6 GHz 5G NR smartphone	20 to 40	1.5 to 2.5 weeks	12,000 to 22,000 EUR
Smartphone 4G + 5G FR1 + Wi-Fi 6E + BLE	40 to 70	2.5 to 4 weeks	20,000 to 35,000 EUR
Two-way satellite handset	10 to 20	1 to 2 weeks	10,000 to 18,000 EUR
Vehicle-embedded phone eCall + voice	5 to 12	1 week	7,000 to 12,000 EUR

The cost depends mainly on the number of operational bands and the number of configurations to evaluate (low, middle, high channel on each band, plus multi-radio configurations). A product with active beamforming (5G FR1 with synchronous multi-antennas) requires angular scanning that can multiply campaign duration by 1.5 to 2. See Certification costs for the overall budget framework of a product certification.

Key takeaways

HAC is a US-specific requirement, with no direct EU equivalent, framed by 47 CFR 20.19 and the ANSI C63.19 methodology.
The universal mandate took effect on 3 April 2024, requiring 100 percent of models rated M3 or higher and T3 or higher.
Two paths coexist. The M rating characterises RF interference at the hearing aid microphone, the T rating characterises the magnetic coupling with the T coil.
HAC and SAR are independent. A product may be SAR-compliant and fail HAC, or the reverse, because the physical quantities, phantoms and measured bands differ.
ANSI C63.19-2019 is the current version, the reference for any post-2023 submission. ANSI C63.20-2019 addresses HAC for wireless audio accessories.
The main pitfall is the late discovery of the requirement during the product cycle, leading to an antenna re-spin or to a costly second laboratory campaign.

For practical application on the US side, see FCC tests and FCC procedure. For the SAR context with which HAC is coordinated, see SAR procedures (IEC 62209, EN 50360). For the definition of the terms M, T, HAC, see the Glossary.