
iPhone audio detectable with AM radio - kimburgess
https://twitter.com/doctorcube/status/1300953606221422594
======
commonjcb
It's probably by design, iPhones support magnetic-induction hearing aids, see
here:

[https://support.apple.com/en-us/HT202186](https://support.apple.com/en-
us/HT202186)

The are 2 standards, the old "telecoil" (direct) and the new FM loop, both
operating at low frequencies...

Both work at very short ranges (inverse cube of the distance)

~~~
angrygoat
Excellent that there is accessibility support, but at what range can people
pick my calls up – especially with a directional antenna?

~~~
commonjcb
Approximately the same distance as a good microphone can pick up the audio
anyway. Read about near-field vs far-field:

[https://en.wikipedia.org/wiki/Near_and_far_field](https://en.wikipedia.org/wiki/Near_and_far_field)

------
amelius
I've found that the iPhone display is quite easily detectable between 400nm
and 700nm wavelengths.

~~~
jwandborg
That sounds way worse since it's in the frequency range of many high-powered
lasers.

It's also in the range of many low-power lasers, but I'm not worried about
them.

~~~
Johnythree
Woosh...

------
IndrekR
Most likely not an FCC (EMC) issue. This sounds like direct inductive coupling
from speaker D class amplifier output (or power, which would be worse, but not
likely) circuit at <100 kHz. Below 30 MHz only conducted emissions are
measured (common mode emission via cable, say, forming a large antenna
together with the power grid). The emitting component may be the speaker or
(unshielded) output filter (for EMC compliance!) of the amplifier.

Why it is not an issue, is that magnetic field decays really rapidly,
(inversely proportional to the cube of the distance [1]) and thus is not a
general concern. In fact some "secure by physics" nearby communication methods
like RuBee [2] relay on this.

[1]
[https://en.wikipedia.org/wiki/Near_and_far_field](https://en.wikipedia.org/wiki/Near_and_far_field)

[2] [https://en.wikipedia.org/wiki/RuBee](https://en.wikipedia.org/wiki/RuBee)

~~~
0-_-0
A later tweet says "I was able to hear it from 20 feet."

~~~
floatingatoll
I can hear the iPhone’s speaker from 20 feet away, too - without using AM
radio technology to do so. (It’s a curse, trust me.)

------
compsciphd
Also happens in the reverse. growing up in the shadow of WTOP[1] towers in the
DC area, we used to hear WTOP in our rotary phones (between dials mostly) and
even sometimes picked up in our ovens (yes, could hear the radio coming out of
the oven)

[1] [https://en.wikipedia.org/wiki/WFED](https://en.wikipedia.org/wiki/WFED)

it was really powerful, heck, I even remember in my youth going up to
relatives in boston and being able to pick up the signal at night to listen to
Oriole games in the summer.

------
m0xte
This is not surprising. We’ve been using AM and FM radios to debug circuits
for decades. They can pick up oscillations and instabilities.

But the range is centimetres at best. So much so the antenna gets used as a
fairly directional probe.

~~~
phlhar
In a later tweet he says the signal is pretty strong and that he could detect
it from 6 feet away

~~~
evgen
Going to have to call bullshit on this. If it was detectable at that range
then he has a faulty phone. The iPhone is classified as an emitter and so it
needs to undergo rather strict FCC testing to ensure that it does not emit
outside of certain frequencies and at specific power levels. The device would
NEVER have been approved if it emitted at this level into bands licensed to
other uses.

~~~
jojobas
6 meters is near field in that frequency range. The emission power is possibly
well below FCC limits.

------
emsy
My neighbor is a Ham radio operator (don’t remember which frequencies are used
in Germany). I sometimes can pick up the incoming radio signal. He explained
to me it’s most likely the amp de-modulating the signal that is fed into the
power line and my headphone cable acting as an antenna. When I first heard
voices speaking I was a little freaked out for a moment I have to admit.

~~~
abyssin
I remember picking up the conversation coming from a hot air balloon one day I
was playing on the computer. I was focused on the game, and suddenly these
voices start overlapping with the sounds I'm used. Today I'm not even sure it
was possible. The speakers were that kind that made a noise when receiving or
sending an SMS from a nearby mobile phone.

------
doctorshady
I'm surprised this wasn't discovered sooner. For a while, when I was working
in Portland radio, there was an AM station that played recent indie releases
on it. Needless to say, while it was the butt of countless hipster jokes,
there was a sizable crop of people with both AM radios and iPhones on them,
frequently operating at the same time.

~~~
evgen
It wasn't discovered because either it didn't happen or the person claiming
such has a faulty device. The FCC would never allow these phones to be
imported for sale if they were so sloppy in their emissions. The idea that
there are millions of people out there listening to AM radio every day for
hours at a time in cars and homes/offices in close proximity to iPhones but no
one ever detected this before is laughable.

~~~
SiempreViernes
Arguments by appeals to authorities like the FCC, CDC, or FAA sort of work if
the authority can be trusted.

For the argument to be coherent that trust must have been established by a
proven track record of both employing the appropriate methods correctly _and_
showing independence of vested interests in their reporting of the results.

~~~
evgen
Apparently you have no idea what you are talking about, so you think that
these sorts of arguments work when discussing FCC emission testing. The FCC
does not actually run the test, they set the standards. The tests themselves
are run by various labs and testing agencies that are certified to perform the
tests and who would be risking a very lucrative gig for the sake of cheating
on a test for a device that will be widely deployed and certainly tested by
third-parties who will want to examine the device. It is possible for some
mid-range device to slip through or bribe someone to pass a test, but unlikely
to the point of absurdity that this would be done for something like an
iPhone.

~~~
SiempreViernes
Hilariously, this is what I found when searching for the public test results
of the iphone8, apologies for it being about a previous generation, but
happily your argument is insensitive to such details:
[https://www.chicagotribune.com/investigations/ct-cell-
phone-...](https://www.chicagotribune.com/investigations/ct-cell-phone-
radiation-testing-20190821-72qgu4nzlfda5kyuhteiieh4da-story.html)

The summary of the above article is that yes: _if_ you hold the phone
sufficiently far away from the measuring device the detected radiation is
below the levels mandated, and if someone else tries to test the emission for
themselves Apple will say they did it wrong and refuse to give any explanation
of what the error might be. A bullet proof system indeed.

~~~
evgen
Lol, 2mm. That is the distance this test used that you claim is some sort of
support for your argument in this case. Sorry, but the only other
corroborating evidence is a later claim made by a company that sells RF-
shielded phone cases. I am going to have to chalk this one up to unclear
guidelines (mis)interpreted by people who do not understand the square power
law.

Try again.

~~~
glitcher
I feel like you may have very good points to contribute, but your dismissive
and combative tone is kinda ruining it for me.

------
swiley
Meh. More fun is listening to the GPU redraw the screen and the cpu servicing
interupts, both of which you can hear by holding an AM radio close to the
phone.

~~~
formerly_proven
For most laptops you don't even need a radio, just ears.

~~~
skim_milk
I can't wait for laptops to start including the 30xx series NVidia cards in it
and replace mine, because my current one is so awfully noisy. The sound of the
USB circuitry in my laptop processing my mouse movements is louder than the
sound of my mouse moving across the mouse pad, and when I'm moving a bunch of
data around the SSD in my laptop makes as much noise as the physical hard disk
it replaced! I am constantly in awe of how noisy some things that aren't
supposed to be physically moving at all can be.

------
geerlingguy
I just tested this on my iPhone XS with both an old AM radio and my SDR
receiver, and neither seemed to cause any kind of signal or interference
around the 930-980 KHz range.

My dad, a radio engineer (who worked for one of the US' largest AM radio
stations for a decade), also tested with his XR and couldn't find any signal.
I'm wondering if either it is limited to the iPhone 7 and/or 8, or if the
Twitter OP might have a faulty unit?

Has anyone else been able to replicate the result?

~~~
floatingatoll
Retest with the hearing aid settings enabled?

[https://news.ycombinator.com/item?id=24363153](https://news.ycombinator.com/item?id=24363153)

 _To activate Hearing Aid Compatibility on an iPhone with iOS 13 or later, go
to Settings > Accessibility > Hearing Devices. On these iPhone models, Hearing
Aid Compatibility modifies the phone’s acoustic settings to improve
compatibility with hearing aids set in "T" or telecoil mode._

 _If you have an iPhone 6 or earlier, you can activate Hearing Aid Mode. To
activate Hearing Aid Mode, go to Settings > General > Accessibility. Hearing
Aid Mode reduces the transmission power of the cellular radio in the GSM 1900
MHz band, which may result in decreased 2G cellular coverage._

------
numpad0
Isn’t it more or less how inductive speakers[0] work?

[0]:
[https://youtube.com/watch?v=vDrRNdgz2C8](https://youtube.com/watch?v=vDrRNdgz2C8)

------
xt00
Pretty interesting.. many class D audio amps drive at frequencies above
100-200khz, so either the odd or even harmonics of that frequency sounds like
where you would get the actual audio content showing up in the audible band
(not sure if it’s odd or even that would be the right one). I want to try this
on some other class D speakers.

------
vmarius
Wow. I wonder how far from the phone this signal could be detected.

~~~
sgt
Just a few meters, as per the article. I'm guessing if you can't hear it on
the iPhone's speaker, it won't be audible on AM radio either.

~~~
m0xte
Correct. Although it’s possible on older handsets with 3.5 jack that the audio
amplifier in the handset itself is possible to receive. I’m not sure about
lightning.

But I very much doubt at the stated range. The EMC guys would be all over
that.

------
jakedata
This feature was also available on the Altair 8800.
[http://vintagecomputer.net/browse_thread.cfm?id=720](http://vintagecomputer.net/browse_thread.cfm?id=720)

------
polskibus
Why does it say it's an FCC problem? What are the consequences that Apple may
face?

~~~
mijoharas
Wirelessly transmitting devices have a lot of regulations on what they can
transmit, they need to be certified by the FCC, and are not allowed to
transmit in certain frequency bands beyond a certain power.

Some of the discussion here is asserting that this is just induction (i.e. a
changing magnetic field causing a changing electric field in the radio, rather
than the radio antenna picking up the signal). if that's the case, I'm unsure
about why the radio would need to be set to a specific frequency to pick this
up (is the proposed inductance in the speaker wire?). Magnetic fields drop off
very quickly (with the inverse square of distance) so this is also why people
are saying this would be a very short range effect.

The other options seem to be a faulty device actually emitting electromagnetic
waves in the stated frequency domain, or an actual fault in general with
iphones emitting at that frequency.

The last one would likely have very large consequences for apple (i.e. iphones
not able to be sold in the US, and then probably most other markets with
similar regulations, i.e. anywhere). Companies tend to be pretty strict on the
testing of these things due to the large repercussions, which is why I assume
people think it's unlikely.

What I don't know is the repercussions for apple producing some faulty devices
that would broadcast EM radiation like that, can anyone fill me in on that?

------
daneel_w
I can do this with my Asus laptop as well, at up to about 5 meters distance.

