The source of the problem was a homemade battery-operated device designed by a local resident to alert him if someone was upstairs when he was working in his basement. It did so by turning off a light.

“He has a fascination with electronics,” Mr. Glassburn said, adding that the resident has special needs and would not be identified to protect his privacy.

The inventor and other residents of his home had no idea that the device was wreaking havoc on the neighborhood, he said, until Mr. Glassburn and a volunteer with expertise in radio frequencies knocked on the door.

“The way he designed it, it was persistently putting out a 315 megahertz signal,” Mr. Glassburn said. That is the frequency many car fobs and garage door openers rely on.

“There was no malicious intent of the device,” he said in a statement.

The battery on the device was removed and the signal stopped. “It was a relief,” Mr. Glassburn said.

It's like how people in the country in most cases can have a wood fire, and it's no problem. Get to the population density of the city, and backyard wood fires become the major source of particulate air pollution. It's like how in the early days of electricity, there were to GFCI safety devices and everything was just bare conductors on ceramic insulators nailed into wood. We're not in those days anymore.

Or is it the power that is limited? (Which makes a lot of sense)

There is almost always a power limit, and there are often spread spectrum, usage type, antenna directionality, and other requirements. Additionally, licensed users need For 433 MHz in the US, you have two allowed usage rules: 47 C.F.R. 15.240 [0] and 47 C.F.R. 15.231 [1]. The former is for transportation use only. The latter is what car remotes use, and your usage probably falls under that as well. Among other requirements, you can transmit for no more than 5 seconds--unless they are signalling an emergency alarm condition. If you don't follow either part there is a very minimal power output that is generally not useful for wireless data transmission.

[0] https://www.law.cornell.edu/cfr/text/47/15.240 [1] https://www.law.cornell.edu/cfr/text/47/15.231

If it's an FCC class B, YOU must accept interference from otherwise approved class B compliant devices. Class B is a very low threshold for that. Mostly it's power limits and not much else.

Key fobs, if you look at the fine print, are Class B.

There are also exemptions for certain experimental or lab devices though you can't break power limits with those as narrowly defined by regulation.

But if you happen to have your Class B device too close such a device, that's entirely your problem, the user of the Class B device.

This is a common issue with ham radio: they actually are allowed to interfere with Class B but it's a political decision that drives most of ham radio to "play nice". Legally they have seniority when it comes to interference and the law when it comes to Class B devices. Basically you are screwed with Class B in most cases with little legal recourse.

And Class B is such a low threshold that 99% of the time such interference is actually due to bad design or use of cheap components in the Class B device itself. In this case, the fobs. Same goes for TVs, broadcast radio receivers, etc.

No one has a right to zero interference from other RF sources for the most part! Mostly because it's physically impossible to assure or deliver! There's merely a regulatory threshold for the extremely bad and summarily interfering levels of RF power.

Regardless of class, spurious emissions are not permitted.

If i remember correctly the main two are: - Power limits - Transmission length per interval of time (I believe max 300ms in any 10s window)

and how it also had unintended consequences. Note how many comments there are from people who don't seem to have understood the disclaimer. I'd bet our rogue dongle-jammer was in much the same boat :)

When you, "make something dangerous easy" you have a responsibility to be very specific in how to use your invention safely. Otherwise disaster seems inevitable.

(Reviewing this comment later I see it can be read in sort of a nasty way; my meaning was that we don't really assign blame to providers of dangerous tools, the low price of razor blades reflects this)

Filtering this stuff isn't hard, but I'm realizing there aren't any good stone-simple tutorials for it. Might have to write one.

If you're running on a dedicated core, as you should, 99% of the time your application just happily runs along.

See also Fourier Analysis on the Wikipedia article: https://en.m.wikipedia.org/wiki/Square_wave

[1]: Yes, so in reality you neither get an infinite set of harmonics, nor a perfect square wave.

Something like this: https://www.aliexpress.com/item/NEW315mhz-rf-Transmitter-and...

So management gets mad at the engineer (who likely has no formal training or knowledge of FCC regulations) and says, "fix it!"

"OK OK I'll just crank up the power!"

Version 1.1 of the board is released on AliExpress a week later ("New version of board. We fixed weak signal!").

End users start getting the new board and like magic they can pick up a signal from like a mile away!

But I highly doubt they will do it :)

An entire bucket of Chinese electronic components in my living room begs to disagree.

Finished goods need FCC certification to be sold.

It would be easy to build a transmitter to blast out a constant high pulse and then just cut it off using a transistor or mosfet hooked up to the trigger on the PIR.

Simple circuit with no microprocessor or coding required.

or wrap it in * to italicize

Edit: OK, I just looked at it on a phone. Yes, it looks bad, and that the lines would have to be about half the length to be readable. Too late to edit this one, but I'll try to switch to italics or '>' in the future for everything except for code samples.

I almost exclusively read HN on mobile, occasionally emailing things to myself to do on a desktop/laptop later.

Avoiding going into the wall isn't overkill, especially if it's cheaper and faster.