# Device That Calls W/O A Ring So THEY Can Listen In? **URL:** \ **Category:** Factual Questions\ **Created:** [May 8, 2002, 3:32pm UTC](https://boards.straightdope.com/t/device-that-calls-w-o-a-ring-so-they-can-listen-in/107910 "2002-05-08T15:32:01Z")\ **Posts on this page:** 6\ **Page:** 2
**Author:** ![Boyo\_Jim](https://avatars.discourse-cdn.com/v4/letter/b/87869e/32.png) [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)\ **Post date:** [May 10, 2002, 8:59pm UTC](https://boards.straightdope.com/t/device-that-calls-w-o-a-ring-so-they-can-listen-in/107910/21 "2002-05-10T20:59:42Z")
That’s it, I knew I read it somewhere. The author, Peter ???, was fairly high up in the British SIS. ---
**Author:** ![Belrix](https://avatars.discourse-cdn.com/v4/letter/b/ed655f/32.png) [@Belrix](https://boards.straightdope.com/u/Belrix)\ **Post date:** [May 10, 2002, 10:58pm UTC](https://boards.straightdope.com/t/device-that-calls-w-o-a-ring-so-they-can-listen-in/107910/22 "2002-05-10T22:58:12Z")
The problem, though, is that a phone is a two-wire device. When you hang up, the two wires are disconnected. The reverse is how the phone company knows to send you dial-tone - when you pick up the phone, you close the circuit, shorting your line toward the central phone switches, tripping a relay, and connecting you to the dial equipment. When the phone is hung up, you have an open circuit and no current flows. No current - no signal. I suppose you could modify the phone to have a high resistance circuit when hung up, allowing a closed circuit when hung up but with too little current flow for the phone switch to trigger - but now somebody is in you house modifying your phone - not part of the original premise. ---
**Author:** ![AndrewL](https://avatars.discourse-cdn.com/v4/letter/a/3d9bf3/32.png) [@AndrewL](https://boards.straightdope.com/u/AndrewL)\ **Post date:** [May 11, 2002, 12:00am UTC](https://boards.straightdope.com/t/device-that-calls-w-o-a-ring-so-they-can-listen-in/107910/23 "2002-05-11T00:00:52Z")
Coincidentally enough, I just finished the final work on a telephone system interface for our company’s equipment… In a standard home phone, there are two systems connected to the wires coming out of the phone jack. First there’s your ring detect circuit, which is basically just a voltage level detector. In the old days the ring detect was just a electromagnetic coil and clapper; these days it’s usually solid-state. Either way that circuit can really only be used to make the phone ring, as it’s not connected to the talk circuit. Secondly you’ve got the voice circuit. As already mentioned in a standard phone this is physically disconnected from the line when the handset is on-hook. No matter what signal you send over the phone line, you’re not making those switch or relay contacts close without someple picking up the phone. Now, office phones are a different matter entierly - they’ve got all sorts of special functionality built in, and some of them can be used as silent intercoms to listen without the handset being picked up. And I suppose it’s possible that some of the newer fancy electronic phones have some kind of hook logic built in to recognize a code sent over the phone line and go into listen mode silently. I’d still want to see a cite before believing it though. ---
**Author:** ![Boyo\_Jim](https://avatars.discourse-cdn.com/v4/letter/b/87869e/32.png) [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)\ **Post date:** [May 11, 2002, 12:30am UTC](https://boards.straightdope.com/t/device-that-calls-w-o-a-ring-so-they-can-listen-in/107910/24 "2002-05-11T00:30:56Z")
If I remember correctly from _Spy Catcher_ (written by a former SIS Officer), it was a device to spy on foreign, probably Russian (I’m speculating here, it’s been quite a few years since I’ve read it) phone systems. So how American or British phones are wired may not even be relevant, because it was designed for other systems. And it would be fiendishly clever that the device, if captured could NOT be turned against the American phpne system. Wait. That’s TOO clever for the CIA or the SIS… Any experts on Communist Bloc phone systems of the 50s and 60s out there? ---
**Author:** ![xash](https://avatars.discourse-cdn.com/v4/letter/x/c6cbf5/32.png) [@xash](https://boards.straightdope.com/u/xash)\ **Post date:** [May 11, 2002, 12:52am UTC](https://boards.straightdope.com/t/device-that-calls-w-o-a-ring-so-they-can-listen-in/107910/25 "2002-05-11T00:52:00Z")
> [@](#): > > \*Originally posted by AndrewL \* > \*\*Now, office phones are a different matter entierly - they’ve got all sorts of special functionality built in, and some of them can be used as silent intercoms to listen without the handset being picked up. And I suppose it’s possible that some of the newer fancy electronic phones have some kind of hook logic built in to recognize a code sent over the phone line and go into listen mode silently. I’d still want to see a cite before believing it though. \*\* Ok, here are some neat counter-measures and phone tap-detectors. i do not vouch for the info or the products mentioned on the site. if you wanna be sure you can order one of the products and see whether they work or not… [http://www.spyemporium.com/product2.html](http://www.spyemporium.com/product2.html) and here’s what i was talking about earlier : [http://www.spyproducts.com/PhoneMonitor1.html](http://www.spyproducts.com/PhoneMonitor1.html) scroll down to “Informer” phone and “X” phone. The “X” phone : "THE “X” PHONE works and looks like a standard telephone. But is also has the capability to function as an advanced remote audio monitoring device. It’s so sophisticated that you don’t even need to call in to see if there’s activity in the area; \ you are immediately and clearly listening to all of the audio activity in the area of THE “X” PHONE. The intruders there have no idea whatsoever that the innocuous-looking telephone over there \ Additionally, this sophisticated unit has the capabilities to provide unprecedented and devastating new options; however, you are warned that it is to be used only in a legal and lawful manner in compliance with all applicable laws and EC.C. regulations. Simple to use, it operates as a fully functioning regular telephone until you activate it. " 349.95$ ! luckily their order page says: “Many of our items are sold only to qualified Federal, State and Local Law Enforcement Agencies. Qualified agencies are invited to write to us on department letterhead for special requests and bids.” so yes, the phone exists (subject to authenticity of website) and you can buy it at 349.95 ---
**Author:** ![Derleth](https://avatars.discourse-cdn.com/v4/letter/d/b9e5f3/32.png) [@Derleth](https://boards.straightdope.com/u/Derleth)\ **Post date:** [May 11, 2002, 1:41am UTC](https://boards.straightdope.com/t/device-that-calls-w-o-a-ring-so-they-can-listen-in/107910/26 "2002-05-11T01:41:24Z")
From _Bigger Secrets_, (William Poundstone, 1986, ISBN 0-395-53008-3) here is the principle behind the infinity box/microphone (pages 85-86): > [@](#): > > Each phone is connected to the phone network via red, yellow, and green wires. The buttons in the phone cradle are switches that disconnect the green wire. A live 48-volt circuit passes through a telephone on the yellow and red wires whenever the phone is on the hook. There is no way to turn a phone completely off, short of pulling it out of the wall. > > The 48-volt circuit rings the phone. The red and yellow wires go to two induction coils and a capacitor. This simple circuit has a resonant frequency of 20 hertz. It’s like a wineglass that vibrates when just the right note is struck. When someone is calling you, the phone company sends out a 20-hertz signal on the red and yellow wires. This signal, which may be very weak, builds up on the phone’s ringer circuit and triggers the ringing mechanism. When you pick up the phone, the circuit drops to 6 volts. > > Since every phone is always electrically live, the properties of the circuit can be measured at any time. An electrical quality called impedance can be measured easily from the phone company’s swiching offices. On a standard phone, this impedance is determined by the two induction coils and the capacitor inside the phone. Extra equipment added to the phone circuit may change the impedance. > > [snip stuff about adding an extra fone, and how the telco gets annoyed at that, and stuff about “babysitter” devices too big to fit inside a phone] > > _Bigger Secrets_ asked [Anthony J.] Caristi [, author of _Electronic Telephone Projects_] about infinity mikes and the Yippies’ claims of eavesdropping on an unmodified phone. He confirmed that infinity microphones are no fantasy. All that’s required is a small microphone hooked into the phone line and drawing, say, 1 milliampere of current, says Caristi. The microphone could be hidden inside the base of the phone, powered entirely by the 48-volt direct current of the phone circuit. It would not affect the normal operation of the phone. > > The 48-volt current comes from continuously recharged batteries at the phone company. Since this voltage is never interrupted, not even during a general power failure, the microphone would constantly impress the room noises on the phone line. Given the 900-ohm impedance of the phone line, a 1-milliampere microphone would produce an audio signal of 0.9 volts in the line. This could be amplified easily. The signal could be picked up anywhere on the phone line–where the wires leave the house, in the basement of an apartment building, at the switching box down the street, or at the phone company switching office. > > All this requires that the phone be modified. According to Caristi, it would be difficult, but probably not impossible, to detect room noises via the ringer circuit of an _unmodified_ phone on the cradle, too. The ringer circuit is not particularly sensitive to ordinary sound vibrations. The resulting “signal” would therefore be extremely weak and difficult to amplify. Caristi conjectures that a well-financed government agency might be able to solve the problems of amplification should is so desire. The Russians are known to have eavesdropped on the American embassy by detecting vibrations in windowpanes, and that would seem no less far-fetched. Interesting. Basic electronics gives you a lot of power (even with only 48 V. :D). [Previous page](https://boards.straightdope.com/t/device-that-calls-w-o-a-ring-so-they-can-listen-in/107910.md?page=1)