How to Make a Phone Tap

Want to impress your friends, family or teacher? An inductive phone tap is a little gadget that can pick up an alternating electric signal from one system (classically a phone line) and copy or induce that signal to be received by a separate output, like an amplifier, with a negligible difference to the phone conversation.^{[1]XResearch source}^{[2]XResearch sourcePankaj, S. <i>Hacking</i>. New Delhi: A.P.H. Pub., 2005. Print.} You should not misuse this device to covertly intercept phone communications, as doing so is illegal in most countries.

Part 1

Part 1 of 2:

Making an Inductive Tap

1
Gather your materials. To ensure that you don't have to interrupt construction of your inductive tap, collect the necessary materials first and prepare your work space. Set up a sufficiently comfortable soldering station that is flat and at an appropriate height. Your target line for you inductive tap should be a standard land line, also known as a POTS telephone. For the construction of your tap, you will also need:
- Enameled copper wire (solenoid wire is ideal)
- Clip-on ferrite
- Denatured alcohol
- Wire cutters
- Shrink wrap wire casing or electrical tape
- Soldering iron
- Solder
2
Open the clip-on ferrite and remove one of the iron cores. Your clip-on ferrite should be comprised of an outer case that houses a magnetic core made of iron oxide and other metals. It is typically dark in color and is often used in electric transformers and inductors where components like your solenoid wire are wound around the inner core.
- Clip-on ferrite is usually shaped so that there is a circular hole through the middle where a cord can pass, and can be opened the side opposite from where the two halves hinge.
- Your core may be circular in shape or rectangular, but it is important you position your clip-on ferrite so that one side is open, much like a book. Without opening the ferrite, it will be difficult to wrap your solenoid wire around the core to make your inductive tap.
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Leave yourself a few inches to spare at each end of the wire. These will be used to connect your jack plug.
4
Replace the core with the coils into the ferrite housing. Now you can use fine sandpaper or some other mild abrasive to remove the enamel coating on the last inch of your wire tips.
- Exercise care when removing the enamel coating. It's easy to nick a wire, but doing so will ruin your inductive tap.
5
Push both wires through a length of shrink wrap, moving the wrap off to the side to insulate after soldering. This will protect your inductive tap against damage and you from shocks from open wires.^{[3]XResearch source} Remember to leave enough poking out of the end so you can connect the jack plug.
- In place of shrink wrap, you can also use electrical tape to insulate your wires.
6
Solder the two 1/8" wires from the jack plug to the ends of your wound wire. Do this by soldering the ends of your miniature phone plug cable to your wire ends. Do not overheat your wire or else it will become brittle and potentially snap off.
- The best soldering joint requires you to prepare the surface by cleaning the area you will solder with denatured alcohol.^{[4]XResearch source}
7
Move your shrink wrap sheath so that it covers the solder joint.^{[5]XResearch source} Cause your shrink wrap to affix closely where you have wrapped it by using a heat source. This will cause your shrink the wrap to shrivel so that it is drawn tight.
- If using a lighter, hold your flame at a distance of about an inch and a half from the shrink wrap.
- If you have insulated with electrical tape, this step should be skipped.
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Part 2

Part 2 of 2:

Installing an Inductive Tap

For your inductive tap to work, you will need a POTS telephone (a standard landline telephone). Remove the plastic casing but be careful not to cut through the wires inside. This will cause your telephone to break, and your inductive tap to not work.
Either of these two wires, which make up the phone line pair, will suffice. You should be careful to avoid the yellow wire. Placing this inside your ferrite will prevent your tap from receiving signal.
A 3.5mm audio extension cable may be needed if there is considerable distance between the tap and the amplifier.
When the telephone is in use, the signal should be transferred to the amplifier through the induction of your phone's electrical signals. Stand back and admire your handiwork as everyone around you calls you a genius.
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Tips

All the necessary equipment for this device can be purchased at somewhere like Maplin (UK) or Radioshack (US). Local electronics and hardware stores are also excellent alternatives.
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The setup may need some tweaking to work correctly. Check for breaks in the wire or enamel left on the ends. Both of these can impede the induction of your signal.
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Instead of wiring your phone tap to a jack plug, you can connect it to an oscilloscope using connecting wires and crocodile clips to see the signal on a display. Even better attach it to a picoscope to allow for analysis of the signal on a computer.
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Warnings

This device is not for use in tapping peoples telephones without knowledge or consent! Unauthorized phone tapping is illegal in most countries and any legal consequences are your own responsibility.
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You should have a basic knowledge of safe electrical practice before attempting to carry out the production of this device to avoid any nasty shocks. The probability of anything in this Wiki being harmful is very unlikely, however it's always better to be safe than sorry.
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