Title says it all. Earlier I was on my old plug-in TT phone (while waiting for the handheld to recharge) activating my credit card, and while hitting the buttons and hearing all the bleeps, wondered if it is possible for someone to hear the bleeps and decipher the number being dialed. Or is each phone different in terms of the notes each numbered button plays?
And on that note and while I’m at it, can someone with a scanner pick up your handheld phone signal and eavesdrop?
Some people can, yes. People with musical ability have an easier time of it, but IMO nearly anyone can train themselves to distinguish DTMF tones. The tones are standard.
The tones themselves (they’re called DTMF btw) are completely standardized - that’s how the central office and/or the computer you are communicating with identify them. There are 2 frequencies for each key in a grid pattern. Back when I programmed IVR systems, I got reasonably good at identifying the tones by ear, so I’m sure someone with training & good pitch could identify the keys easily.
Oh, yes. I bought my scanner for aviation purchases we we live in an apartment building. I was playing with it when I found out that it could pick up cordless phones with no effort. All I had to do was hit scan in the cordless phone range and it always picked up a call. I heard quite the conversations over the next few days before I got tired of it.
The tones themselves are what does the dialing rather than the buttons. You can play a recording of them to make a call. A talented person or maybe a parrot could place calls by voice.
Oh, and to address this: the answer is it depends, but probably not. Unless you have an older analog cordless phone AND the person trying to listen in has either an older scanner, or one that has been modified to receive cordless phone signals you’re pretty safe. Scanners since the mid-ish 90s do not have the ability to receive cordless or cell phone frequencies, per FCC mandate. It is possible to intercept digital spread spectrum transmissions, but the people who know how to do this and have the specialized equipment to do it have better things to do than listen to you on the phone.
If you mean cell phones, on the ohter hand, then almost certainly not with just a scanner. Again, anyone capable of this has better things to do with his time.
Unlikely, since the sound is a combination of tones at different frequencies; that’s hard to do with the human voice.
It sounds a bit like the sound that you can make if you whistle and hum at the same time. It strikes me as difficult but possible to mimic such a sound with no mechanical assistance.
Right, but two people *together *can do it. It was one of my brothers’ favorite stupid party tricks. Actually, they whistled, rather than voicing the tones.
Just in case the Wiki article wasn’t clear…
Each column in the pad is assigned a tone, and each row in the pad is assigned a tone. the tones are standard across all phones. Press a button, and the phone plays both the row and column tones at the same time, identifying which button was pushed.
Wait a sec, so each of my stupid brothers only had to learn *three *tones - and then they were just mixed and matched? Huh. Well, that doesn’t sound so hard for any pair with a decent sense of pitch. Here they had us believing they had spent months “cracking the phone code” or something.
Well one of them had to lean 4 tones or they skipped phone numbers with 0.
Here are the frequencies, in case anyone cares. There are actually four column tones; the fourth one is not used on regular POTS telephones which of course have only three columns. The mysterious fourth column was used on some proprietary PBX systems (before digital signaling) and several military phone systems.
Columns: 1209Hz, 1336 Hz, 1477 Hz, 1633 Hz
Rows: 697Hz, 770Hz, 825Hz, 921Hz
So if you want to dial a 3, that’s the third column and first row, therefore 1477Hz + 697Hz. Easy as pie.
ETA: The dial tone is also two tones – 350Hz and 440Hz. 440Hz corresponds exactly to the standard note A above middle C. All the other tones in the system are slightly off from musical notes in the standard 12-tone system.
:smack: Of course.
Math is the reason I was a Psych. major.
The other trick (I believe) is that on an older phone you can press two buttons at the same time, and hear just the tone for that row/column. The new computerized phones don’t seem to do that, but I think I recall Mr Wizard, or some similar dude doing it on TV way back when.
Anyone with a recording can play it back and figure it out.
In Intro to Signal Analysis, one of our early assignments was to take a recording (with lots of other noise in it) and extract the phone number in Matlab. A few months ago, I was listening to one of the early Dan Savage podcasts, and he called up one of the people who has called in. The tones he was dialing were clearly audible. I was shocked, since anyone with that recording could figure out who had called in (it’s a sex advice column, if you’re not familiar with Savage Love, so privacy is pretty important). I tried to find contact information, but found that that episode had been pulled and recut to not include the telephone tones.
In particular, it was for the military Autovon system, which was abandoned. The 4 extra keys allowed the specification of precedence levels on calls which would knock lower precedence calls down if no lines were otherwise available:
Way back when, when God was still in heaven, before Judge Green, the entire telephone network operated on those tones. So did the features of office PBXs. People who practiced enough could easily tell what number was dialed by listening, and supposedly, there was even one guy who could vocalize the tones closely enough to put a call through. Phone hackers could record or fidgit with the phone to do all sorts of mischief - free phone calls were the least. They liked to do things like route a call to the local pizzeria through Moscow, Tokyo, Mexico City, wherever before ordering extra pepperoni. It might be an urban legend, but I understand that at one point, AT&T sent some of its minions out to local libraries across the country to remove the pages of any book or periodical that had listed the specific tones. Too many people had started to hack in. Now hackers have something better to do.
Not exactly. While it is true that scanners now come with the older, analog, cell phone frequencies blocked out, the cordless phone frequencies can still be received. On the other hand, most new cordless phones are digital and/or encrypted, so there’s nothing to be heard. But the new scanner I bought last fall still stops when it runs across the older phones in use in the neighborhood.
From Wikipedia:
You guys ever heard of Captain Crunch?