Written and maintained by CASRAI Editorial Board
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This page describes products and general use; it is not medical advice.
An FM system is an assistive listening device that sends a speaker’s voice by radio from a microphone and transmitter to a receiver worn by the listener, so the voice arrives with less competing room noise. This page is for clinic staff, buyers and students who need a clear reference for what the product is, how it differs from other assistive listening systems, and how it is classified by the US Food and Drug Administration (FDA).
What an FM system is
The National Institute on Deafness and Other Communication Disorders (NIDCD) states that FM systems use radio signals to transmit amplified sounds. They are often used in classrooms, where the instructor wears a small microphone connected to a transmitter and the student wears the receiver, tuned to a specific frequency, or channel. A classroom FM system is therefore the same product class used in a school setting, not a separate technology.
Who uses it: people with hearing loss, including students who follow an instructor’s voice through the receiver; clinic and school staff who supply and set up the equipment; and buyers comparing assistive listening options. Personal FM systems work the same way as larger systems and can help a person follow one-on-one conversations (NIDCD).
How an FM system works
A peer-reviewed review of assistive listening systems (Pan-ngum et al., The Scientific World Journal, 2013) describes these devices as helping hearing-impaired people by reducing the effects of ambient noise and distance on sound travel. A transmitter is placed near the sound source and a receiver is worn by the listener. In an FM system the signal is frequency modulated onto a radio-frequency carrier wave, and the receiver is tuned to the same frequency. Because the microphone stays close to the talker, the system maintains the signal-to-noise ratio of the source.
- Transmitter and microphone: worn or placed by the speaker (NIDCD).
- Radio link: a specific frequency or channel shared by transmitter and receiver (NIDCD; Pan-ngum et al.).
- Receiver: worn by the listener. NIDCD states that people whose hearing aid or cochlear implant has a telecoil may also use a neckloop or silhouette inductor, which converts the signal into a magnetic signal the telecoil can pick up.
NIDCD states that FM systems can transmit signals up to 300 feet and can be used in many public places.
FM systems and hearing aids
An FM system is a separate listening device that can be paired with a person’s own hearing aid or cochlear implant through a telecoil, using a neckloop or silhouette inductor as described above (NIDCD). For the part of a hearing aid that sits in the ear, see the guide to earmold types. For the supplies a clinic stocks around this equipment, see the audiology clinic supply checklist.
FM vs hearing loop vs infrared vs personal amplifier
| System | How it carries sound | Characteristics stated by NIDCD |
|---|---|---|
| FM system | Radio signals | Transmitter plus receiver on a set channel; up to 300 feet; radio signals penetrate walls, so listeners in different rooms may need different channels |
| Hearing loop (induction loop) | Electromagnetic energy | Four parts: a sound source, an amplifier, a loop of wire, and a receiver |
| Infrared system | Infrared light | Signal cannot pass through walls; cannot be used in environments with too many competing light sources, such as outdoors or strongly lit rooms |
| Personal amplifier | Amplifies sound for the listener | About the size of a cell phone; increases sound levels and reduces background noise; useful where other systems are unavailable |
Source: NIDCD, Assistive Devices for People with Hearing, Voice, Speech, or Language Disorders, checked 2026-10-30.
How FM systems are regulated in the US
Under 21 CFR 874.3320, a group hearing aid or group auditory trainer is a hearing aid intended for use in communicating simultaneously with one or more listeners having hearing impairment. FDA’s device classification database (via openFDA, checked 2026-10-30) lists product code EPF as “Hearing Aid, Group And Auditory Trainer”, device class 2, under regulation number 874.3320. The regulation places the device in Class II (special controls) and exempts it from premarket notification (510(k)), subject to the limitations in 21 CFR 874.9. Whether a given FM product falls under this classification depends on its intended use, as defined in the regulation. For background on the law behind device classes, see Medical Device Amendments of 1976, and for post-market problem reporting see medical device reporting (MDR).
Safe use and handling basics
- Match the receiver and transmitter to the same channel; the radio link only works when both are tuned to the same frequency (NIDCD; Pan-ngum et al.).
- Where several rooms use FM systems close together, expect that radio signals can pass through walls, so rooms may need different channels to avoid mixed signals (NIDCD).
- Follow the manufacturer’s instructions for use for charging, cleaning, battery handling and fitting; this page does not replace them.
- Questions about hearing, fitting or settings for an individual belong with an audiologist or other qualified clinician.
Common mistakes
- Assuming a radio system stays inside one room. NIDCD notes that radio signals penetrate walls, which is the reason separate channels are used. An infrared system is the type NIDCD describes as unable to pass through walls.
- Treating all assistive listening systems as one product. FM, loop, infrared and personal amplifier systems use different carriers, as the table above shows.
- Expecting a telecoil connection without the accessory. NIDCD describes a neckloop or silhouette inductor as the way a telecoil picks up the signal.
FAQ
What is an FM system?
An FM system is an assistive listening device in which a talker’s microphone and transmitter send amplified sound by radio signal to a receiver worn by the listener (NIDCD, checked 2026-10-30).
What is a classroom FM system?
It is an FM system used in a classroom: the instructor wears a small microphone connected to a transmitter and the student wears a receiver tuned to the same channel (NIDCD).
Can an FM system be used with hearing aids?
NIDCD states that people with a telecoil in their hearing aid or cochlear implant may use a neckloop or silhouette inductor to convert the FM signal into a magnetic signal the telecoil can pick up.
How far does an FM system reach?
NIDCD states that FM systems can transmit signals up to 300 feet.
Is an FM system an FDA-regulated device?
Group hearing aids and group auditory trainers are classified under 21 CFR 874.3320 as Class II devices, exempt from 510(k) premarket notification subject to the limitations in 21 CFR 874.9 (eCFR, checked 2026-10-30).
Sources
- NIDCD, Assistive Devices for People with Hearing, Voice, Speech, or Language Disorders, checked 2026-10-30.
- eCFR, 21 CFR 874.3320 Group hearing aid or group auditory trainer, checked 2026-10-30.
- FDA device classification via openFDA, product code EPF, api.fda.gov, checked 2026-10-30.
- Pan-ngum et al., The Scientific World Journal, 2013, PMC3676962, checked 2026-10-30.
