Re: The FIREWALL CHIP. U're phone always offhook?

You wrote: 

>>    We have potential bugging devices in all our houses - The telephone!
>> Of course, when it is onhook, the microphone does not transmit... or
>> does it? 
>
>The Mondo article ("Total Surveillance" by Charles Ostman) was a joke.
>
>From the innacuracies in what I do know about, I assume all of the
>phone-paranoia is also unjustified.

Actually, there is a germ of truth in this.  On older phones (don't know if 
this works on newer electronic phones) when the handset is 'on-hook' a 
switch opens and breaks the voice circuit.  This of course only works for 
DC circuits.  If you drive that same circuit with an AC signal (from 
further up the line) then that 'open' switch becomes a capacitor and acts 
as a band-pass filter.  Signals from the mic will then modulate that AC 
current and can be extracted and reconstructed.  Supposedly the Dutch 
police have perfected this and use it in investigations to circumvent legal 
restrictions on physically bugging suspects homes; or so was alleged a 
couple of years ago during a narcotics trial in Amsterdam.

Dale H.

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                          SANDY SANDFORT
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C'punks,

On Thu, 2 Feb 1995, Dale Harrison wrote:

> . . .
> Actually, there is a germ of truth in this.  On older phones (don't know if 
> this works on newer electronic phones) when the handset is 'on-hook' a 
> switch opens and breaks the voice circuit.  This of course only works for 
> DC circuits.  If you drive that same circuit with an AC signal . . .

There's another angle I may have mentioned before.  Many 
electronic phones come with a ``feature'' that allows you to 
call home, produce an electronic tone and eavesdrop on your own
house.  When the tone is sounded, the ringing stops (or never
starts) and the phone goes into ``off hook'' mode (i.e., the
microphone in the mouthpiece is turned on).

Even if you did not buy this feature when you bought your phone,
it is still there, just waiting for that electronic tone.  You 
can't produce it, because you didn't buy the doohickey, but anyone
with such a doohickey can call your house and listen in. . .


 S a n d y

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From a couple of folx....

> > Actually, there is a germ of truth in this.  On older phones (don't know if 
> > this works on newer electronic phones) when the handset is 'on-hook' a 
> > switch opens and breaks the voice circuit.  This of course only works for 
> > DC circuits.  If you drive that same circuit with an AC signal . . .
> 
> There's another angle I may have mentioned before.  Many 
> electronic phones come with a ``feature'' that allows you to 
> call home, produce an electronic tone and eavesdrop on your own
> house.  When the tone is sounded, the ringing stops (or never
> starts) and the phone goes into ``off hook'' mode (i.e., the
> microphone in the mouthpiece is turned on).
> 
[ Snip! ]

A simpler solution is to keep the phone in another room used mainly for
phonecalls, or even in a small office if you don't make an sounds there
worth evesdropping on. (The really paranoid can soundproof/tempest-proof
the room....)