
"I would dial the 300 baud dial-up number, and scream the carrier tone." - pavel_lishin
http://blogs.msdn.com/b/oldnewthing/archive/2011/11/11/10235970.aspx
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ddlatham
I have a very low voice and enjoy singing or humming along with the bass line
in music some times. While I was singing along with a song, all of a sudden my
monitor started to go a bit nuts and wave. When I stopped singing (or changed
notes) it stopped.

I turned to my roommate, "Can you see that?"

"Nope."

It turned out that if I sang a note at the same frequency as my monitor's
refresh rate, the image on the screen would start to modulate up and down in a
wavy sort of way. But to my eyes alone. Must have been something with the
motion of my eyes or my head matching the refreshing of the screen.

~~~
bronson
I think that's exactly right. Try chewing crackers or chips (the crunchier the
better) while looking at an LED clock (like a microwave). Most work, depends
on refresh rate. There's a good chance you'll see the same sort of waviness.

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user24
blowing a raspberry achieves the same effect.

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burgerbrain
And now my screen has tiny specs of spit on it.

Well played sir, well played.

~~~
user24
it really does work with things like alarm clocks.

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burgerbrain
Yeah, it does. Tried it with my alarm clock and got it to work. Just thought
I'd remind people to think before trying it on their computers. ;)

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jgrahamc
I used to pulse dial a phone using the hook switch to get free calls. There
was a phone in the bar in my college that only accepted incoming calls. It did
this by having no dial. Of course, that didn't stop you from tapping out the
phone number if you could get the beat right.

The other stupid phone that I hacked around was a pay phone in a flat that I
rented where you'd pick up the handset and get a dial tone but the keypad was
inoperative unless you put in money. Hello DTMF pocket dialer.

It's not unreasonable to think that someone could emulate the carrier tone
with their voice. After all the modem had to work inside the frequency range
used for voice communications.

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DanielBMarkham
I think I read somewhere that the system was designed specifically for this
kind of attack. It uses two tones of widely different frequencies.

Of course, if you had a friend....

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chronomex
The tones used in DTMF were chosen to minimize _accidental_ talk-off. They're
relatively widely separated, with no harmonic relationship between any given
pair.

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kstenerud
When I was a kid, I'd load executables into a text editor or hex editor to see
what was inside. I quickly figured out how to identify uncompressed graphics
and audio data by sight, and to identify various opcodes by their ASCII
interpretation. It made ripping and patching a lot quicker since I could
eyeball it first before deep diving, and made it trivial to find encrypted
portions in the executable.

I still do it sometimes.

Another, less useful skill (now) was the ability to detect a failing floppy
disk by resting my hand on top of the drive while it was reading. I also
resurrected a couple of seized hard drives by opening the case and spinning up
the platter with my finger, much to the shock and dismay of onlookers.

~~~
meric
>> I also resurrected a couple of seized hard drives by opening the case and
spinning up the platter with my finger.

Cool. So the speed of the spinning does not need to be some constant?

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kstenerud
You just need to get the drive spinning. The motor will set it to a constant
speed, but when the drive has seized, it can't start the platter spinning to
begin with.

However, once you open the drive, you have VERY limited time to copy the data
off since it's designed to run in clean room conditions (internally).

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bitwize
I could hear the extremely high-pitched capacitor singing in many CRTs,
allowing me to determine before I walked in a room if there was a TV or
computer monitor on.

It was awesome. Felt like my very own mutant power.

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BCM43
I think a lot of children can do this. I remember in middle school the entire
class complaining that the TV was on, with a blank screen, and the teacher
having no idea how we knew.

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gchucky
It has to do with how hearing degrades as a person ages. Some places use this
to their advantage and install devices that emit high pitches so as to stop
teenagers from loitering there. I know the Ikea in Brooklyn has it, for
example.

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sneak
Problem is, as I aged, all the CRTs disappeared. So which is it?!@!1!?

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jscheel
When I was a kid, I took apart an old VHS deck. One of the huge ones, from
when they first came out. Not sure what I thought I was doing, but I proceeded
to attach the output of the transformer into the transmitting portion of an
old rotary phone I had also disassembled. Our phone line went dead. According
to our neighbors, our subdivision's entire phone network went down too. Not
sure if that's true or not, but I am definitely surprised I didn't burn down
the house that day.

~~~
brk
If I am not mistaken this was the essence of the (fictional) 'blotto box'. The
recipe entailed hooking a power generator into a phone trunk line and taking
out the majority of a subdivisions phone circuits. I was written up in many of
the phreaker/anarchy text mags that were popular at the time, but I never
heard of anyone actually trying it. I'm also pretty sure the authors were not
aware of things like fuses...

Brings back fond memories though.

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iterationx
Order a pizza from the campus online computer, crash computer, call inquiring
about the status of said pizza, receive many apologies and a free pizza. Not
proud of it anymore though.

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ngvrnd
I used to be able to tell which of the long row of Model 33 TTY's was left on
at the college computer center by whistling the 300 baud carrier and
modulating it a little. The ones that were on would start typing gibberish.

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davepm
Some of us radio hams still whistle up a repeater station instead of sending
the (normally) 1750hz tone to activate it!

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ctdonath
A friend would call with his computer out of the blue. I'd hear the tone, and
whistle the matching tone back to keep it happy until I could get my own
computer up and running to link up.

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lowglow
Back in my phreaking days, I was grounded so often that out of sheer boredom I
learned to whistle DTMF tones. I could dial a number simply by whistling it.

~~~
pavel_lishin
I thought the key word in "DTMF" was "Dual"? How do you whistle two
frequencies at once? Or was the receiving end just very forgiving?

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colanderman
Mongolian throat singing.

~~~
Stratoscope
You can't generate DTMF tones with throat singing. I do some throat singing,
and a better name for it is overtone singing. You're not producing two
different fundamental tones as DTMF would require, you're producing one
fundamental tone and then emphasizing and suppressing various harmonics
(overtones).

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SODaniel
I used to run a BBS in my teens (USR 2.400 -> USR 56k modems -> ISDN) and can
still hear exactly where in the handshake a connection fails.

It's my only super power :(

~~~
mavrc
I also used to run a BBS. We had a small enough userbase (a couple hundred
folks, with maybe 30-40 real diehards) and modem tones were unique enough
above 14.4K that I could tell with reasonable certainty whom was calling in at
any given time. I don't know if this would scale but it was pretty handy for
freaking out anyone who happened to be hanging out in the computer room.

Also, at no point did I abuse my local console access powers to cause people
to fly into heavily fortified sectors in Trade Wars. That would be mean.

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Argorak
From the comments:

"I used to be able to tell whether a CRT monitor or TV was on or off being in
a different room. I guess I could hear the 50Hz?"

I am able to do this as well and usually attribute that to the fact that I
grew up in a household without a TV. I could enter a house and immediately
tell whether someone watched TV in the basement. Now, the question I have that
I never got around asking:

Is this due to most people just not being able to hear those frequencies or
just the fact that this sound is so common that most people just don't notice
it anymore?

~~~
justincormack
I could too but dont think I can anymore as have got older, though hard to
find a crt to check. Suspect a lot of people just could never hear that high.

Though curiously I grew up without a tv too...

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rbanffy
I grew up with TVs and still can hear most of the CRT sets. It's because,
IIRC, the horizontal sync frequency is around 15KHz which is higher than what
most people hear. The sound gets significantly louder when the TV loses
signal. The same happens with NTSC/PAL frequency computer monitors (I restore
and collect vintage computers, so I have a healthy collection of those).

Oddly, some higher resolution screens (XGA and above) also emit a high pitch
noise. Unless there is some frequency multiplication going on, they shouldn't.

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ggchappell
I've done this, too. Only I would whistle. Start low and gradually rise.
Eventually I'd hit the right frequency.

The application was when I answered the phone and heard nothing. Sometimes it
was a spurious call from a modem. Maybe a wrong number. Maybe a friend
thinking I'd be available for a chat (houses usually had just one phone line
back then).

BTW, I'm not sure I quite believe the story from the post. If my memory serves
me correctly, it is the _answering_ modem that would produce a tone first.

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marshray
Yep. I did that too.

I was younger and my voice hadn't changed so it wasn't so much of a scream,
more of a loud "Eeeeeeeeee...". Though I doubt it was any less annoying to the
adults around.

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lostlogin
I can make a fairly accurate guess of what type of scan an MRI scanner is
running by the noise it makes. T2, PDFS, T1, types of gradient echoes etc. I'm
not alone in this and know a fair few people who can. I have managed to tell
when a scan is badly set up with this technique too, really surprises people!

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DanBC
I used to live in a small village with a "party line".[1]

People would know if you just picked up the handset, but you could put the
phone on a bowl to listen in on other people's calls.

[1] (<http://en.wikipedia.org/wiki/Party_line_(telephony)>)

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micheljansen
I could - and still can - make a pretty damn good estimation of a CRT
monitor's refresh rate. I can distinguish between 60Hz, 80Hz and 100Hz with
reasonable accuracy (in steps of about 20Hz). Also, anything below 80Hz gives
me terrible headaches.

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marquis
I badly want to hear a recording of this.

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mmaunder
I spent hours as a young phone phreak trying to sieze an international (phone)
trunk by whistling 2600hz like cap'n crunch did to sieze 800 trunks in the US
and get free phone calls. It never worked because to sieze an international
CCITT5 trunk you'd use a combo of 2400/2600hz. But I did it anyway when I was
bored and tried to modulate a bit of 2400hz in there - figured one day I'd get
lucky.

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e03179
In the early 90's I used an old VCR tuner (over the air) to listen to
telephone conversations people were making. I lived in an extremely rural area
and had few neighbors.

~~~
laconian
I did something similar to this. I found that if I held down the talk button
on a walkie-talkie and crossed its antenna with that of a portable TV, I was
able to tune into analog cellular calls. I would adjust the frequency on the
(analog, nondiscrete) TV tuner to listen to different calls.

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scg
I can ballpark the RGB components of any color. :)

