Harm in the spec specifically means personal injury or leading to personal injury. Headphones not working is an inconvenience. Let’s not get ahead of ourselves here.

No. The FCC definition of harmful is easily searchable but it is basically the same as the Canadian (Industry Canada) definition - the FCC definition is more specific about safety-related systems including radio navigation systems:

"endangers the use or functioning of a safety-related radiocommunications system, or significantly degrades or obstructs, or repeatedly interrupts, the use or functioning of radio apparatus or radio-sensitive equipment."

The whole reason that these systems (Bluetooth, Wi-Fi and unifying) use 2.4GHz is because it’s unregulated.

So if one Bluetooth device interferes with another, but not other bands, then it won’t be breaking any laws. But it might be breaking a contract about the use of the Bluetooth or Wi-Fi logos.

Important distinction: the 2.4 GHz spectrum is _unlicensed_, not unregulated. E.g. ETSI EN 300 328 regulates bandwidth usage, duty cycle, output power and so on in the EU. Products carrying the CE mark should adhere to these standards.

> Products carrying the CE mark should adhere to these standards.

And what evidence is there that Logitech MX products don't?

The whole point of 2.4GHz band is to be a "dump" band due to interference from microwave ovens, and happens to be a global band because of microwave ovens on airliners.

I'd love to hear the history of it, because my understanding was that the 2.4 GHz band would be useless for long-distance communication even without microwave ovens, due to atmospheric attenuation. That is, 2.4 GHz is useful for microwave ovens and useless for long-distance radio for the same reason, because they are easily absorbed by water.

Essentially when microwaves were introduced the 2.4GHz spectrum wasn't allocated from my understanding, and USA proposed the current allocation as global one so that nobody would try to depend on it and then suddenly face interference from airliner's microwave oven (for example while on the ground) - this move preempted various legal issues of including the devices in airplane equipment and probably made for easier spread of microwave ovens in general as they got cheaper (because less certification etc.)

Thank you, and I hadn't known that part of the history. I knew that microwave ovens could cause issues, especially for older models with poor shielding or if the door is opened prematurely, but hadn't realized that was the reason it stayed unlicensed.