The Legality of Personal FM Transmitters

How FM transmitters are regulated and what you need to know.

Man in handcuffs in front of car

Vstock LLC / Getty Images 

Given how heavily regulated the radio spectrum is, are you breaking the law if you listen to music from your iPhone when it's plugged into a personal FM transmitter

Radio broadcasts are heavily regulated throughout the world, and in the U.S. the FCC has that responsibility. 

In theory, any device that bears that label is legal, both in terms of its manufacture and in terms of its use. However, the issue is a little more complicated than that. The chances of you ever “getting in trouble” for buying and using a device that breaks or bends the rules is extremely unlikely, but the fact is that a lot of transmitters either flirt with or outright break the FCC rules.

FM Transmitters and FCC Regulations

In the United States, the portion of the radio spectrum that lies between 87.9 and 107.9 MHz is set aside for FM radio broadcasts.

The intent of the FCC's regulations is to prevent an electronic device from pumping out garbage interference that could potentially interfere with radio, television, and other official uses of the radio spectrum. There are specific limits as to how much interference a device can generate, and devices that conform to the relevant regulations can be stamped with an FCC mark.

If a personal FM transmitter meets the FCC's guidelines for FM, it will carry the “FCC Declaration of Conformity,” which states that the device in question has been tested and verified to meet FCC limits on RF emissions. Here's the declaration:

“This device complies with part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation.”

However, even if you buy an FM transmitter that bears a statement of conformity, there's no guarantee that it actually does. According to a study performed by NPR Labs, about thirty percent of the transmitters they observed in the wild exceeded FCC limitations on broadcast power. In fact, NPR fought for a long time to stop companies from producing and selling overpowered FM transmitters.

Accidental Pirate or Innocent Consumer

The penalties for producing and selling overpowered FM transmitters are extremely steep, but they apply to the manufacturer and not the consumer. It is extremely unlikely, given the number of FM transmitters out there, and the mobile nature of using one in your car, that the FCC would have the resources or ability to track you down even if they cared. Operating a stationary, powerful transmitter is what tends to get people in trouble. 

That said, tuning your FM transmitter to an empty frequency is good for you and your fellow commuters. Your music will sound a lot better, won’t suffer from interference, and the guy in the car next to you won’t have to listen to it popping in and out while he’s trying to listen to NPR. Some transmitters can actually scan for an empty frequency automatically, and there are also a few different steps you can take to improve your FM transmitter experience even if your device lacks that type of functionality.