I am implementing the following circuit

enter image description here

but I am stuck at one point.

How can we input the wires in IN1 , IN2, OUT1, OUT2? I don't know which wire to insert because there are almost 4 or 5 wires inside the telephone wire. So which wire should I insert in the respective areas?

And is there any alternative for the antenna because it is short in market. :)


1 Answer 1


Image not posted as encouraging use is not considered wise technically or otherwise.

The device shown will land you in jail if used on a telephone system in most countries in the world. "Wire tapping" seems to be highly disliked by almost everyone. For private use the device may have its place but you probably want a more competent circuit.

This device is made to be line powered by inserting it IN a 2 wire line by breaking the line. Cut both line wires, connect one pair to IN1, IN2, connect other pair to OUT1, OUT2. Polarity does not matter. Even IN and OUT are swappable.

This device drops 2 x diode drops plus V = i_line x 200 ohms plus an unknown transmitter_on voltage drop across the bug. It would interfere with line operation in many cases (maybe all) and would be very detectable by any even vaguely competent detection system. It is possibly useful as a concept demonstrator but nothing more.

Aerial, which you did not give an example of, can be a piece of wire. For maximum range there are special needs but this is so non ideal that it matters little.

If you REALLY want to tap a phone line with an RF bug that is line powered it should connect to the line with 2 wires, not break the line, run on the available 50V or 24V and pick audio off the two wire pair. You go to jail for using those also.

  • \$\begingroup\$ Isn't there a way to connect its input and output to the socket designed for modern phone connector. \$\endgroup\$ Jun 9, 2012 at 17:20
  • 1
    \$\begingroup\$ @UmerFarooq - yes - how to connect it to a modern phone is done the same was as to an older style phone. Gaols / Jails used tend to be only old style though. I'd suggest searching for eg "phone bug" for a circuit designed for 2 wire use. Without more information on intended use I will probably not be doing that search for you. \$\endgroup\$
    – Russell McMahon
    Jun 9, 2012 at 21:12

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