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PICList Thread
'[EE:] Mobile Phone'
2001\01\08@121504 by WALSH, Scott

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I have seen a couple of products that claim to be able to warn you that your
mobile phone is about to ring, does anybody have a clue as to how these
things work?

regards,
SW.

NB. The orignal version of the e-mail bounced as I had not included [EE:] in
the subject. :-( Hopefully this time was succesful.

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2001\01\08@140035 by hard Prosser

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My theory on this is that when a cellphone is called it replies to the
cellsite that it has received the call - is turned on, in range etc.
Therefore, it is only necessary to look for a local high field strength
signal in the appropriate frequency band   to deduce that the phone is
answering.
Presumably, once the cellphone has replied, a string is sent containing the
actual type of call - text message, voice etc. before the phone actually
starts ringing.

The above is mostly guesswork but I do have a "Wireless World - Dec 1998"
circuit that seems to work on this principle.

I guess you'd also get a ring indication when turning the phone on and if
moving between cellsites - or maybe these checkins are of very short
duration.

Richard P




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I have seen a couple of products that claim to be able to warn you that
your
mobile phone is about to ring, does anybody have a clue as to how these
things work?

regards,
SW.

NB. The orignal version of the e-mail bounced as I had not included [EE:]
in
the subject. :-( Hopefully this time was succesful.

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2001\01\08@170143 by P.C. Uiterlinden

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"WALSH, Scott" wrote:
>
> I have seen a couple of products that claim to be able to warn you that your
> mobile phone is about to ring, does anybody have a clue as to how these
> things work?

As far as I know, they respond on the strength of the electromagnetical
field, caused by the phone when it starts transmitting as a response
to an incoming call.

That also explains why these products are not selective: they respond
to any phone which is close enough.

Paul.

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2001\01\08@171357 by Nathan D. Holmes

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On Mon, 8 Jan 2001, P.C. Uiterlinden wrote:

> As far as I know, they respond on the strength of the electromagnetical
> field, caused by the phone when it starts transmitting as a response
> to an incoming call.

I'd believe it - my CD player goes nuts (puts out nothing but
static) about 1-2 seconds before my phone rings in my truck.  Would
imagine that the phone is increasing its transmission power to acknowledge
teh tower, because once the call connects, the static goes away
(indicating the phone may have backed the power down - I seem to
remember that many digital CDMA/TDMA phones can change their output
power so they only transmit as much as is needed to make themselves
"heard"...)

(back to lurking now, but just had to comment on this one)

Nathan

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2001\01\09@065946 by Bond Peter S-petbond1

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> I'd believe it - my CD player goes nuts (puts out nothing but
> static) about 1-2 seconds before my phone rings in my truck.  Would
> imagine that the phone is increasing its transmission power
> to acknowledge
> teh tower, because once the call connects, the static goes away
> (indicating the phone may have backed the power down - I seem to
> remember that many digital CDMA/TDMA phones can change their output
> power so they only transmit as much as is needed to make themselves
> "heard"...)

Sorry - I *should* have mentioned I was only burbling about GSM... (and
DON'T talk to me about 3G!!!)

Peter

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2001\01\09@100116 by aipi Wijnbergen

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Hi Scott,

Elektor Electronics published an article a few months ago describing a
circuit that would indicate an in coming call.

Chaipi


At 17:11 08/01/01 +0000, WALSH, Scott wrote:
{Quote hidden}

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2001\01\24@183226 by Paul Erkiert

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If you have an audio amplifier near a mobile phone then you can often hear
the phone handshaking the base, Just before a call rings you hear quite a
distinctive series of busts then a continuous signal as it rings I guess the
device you speak of picks up these transmissions using a simple diode probe
detector. PS try and put your phone near the typical amplified computer
speakers.
{Original Message removed}

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