Spy Review

This is the first of a technical series of articles relating to surveillance equipment. In this article, I’m going to talk about the 2 main types of telephone taps and where they should be located to be effective for monitoring telephone conversations.

When I refer to telephone taps, I mean a device that is connected to the telephone line to enable you to listen to conversations. This might be a hardwired device connected to a tape recorder, or it might be a transmitting device. You can have series and parallel versions of both hardwired and transmitting devices. Typically, transmitting telephone taps are series devices. Hardwired telephone conversation recorders are typically parallel devices.

The distinction between series and parallel devices is how they are connected and what they intercept. This article aims to help you understand how the series and parallel devices work.

How Series and Parallel Telephone Taps are Connected

A series telephone tap involves inserting the bugging device between the telephone and the telephone line. There are 2 wires that carry the audio signal in a telephone line. In the UK, the wires are numbered 2 and 5.

To install a series phone bugging device, you need to disconnect one of these wires from the socket, connect one end of the bug to the telephone wire, and the other end to the socket wire. In the UK, you can use either wire 2 or wire 5, it doesn’t matter. Think of it as the electrical signal flowing through the bugging device.

A parallel telephone tap is very different, and means you don’t need to disconnect any wires at all. You connect each of the wires of the parallel bugging device to each terminal. So, for the UK, you connect one device wire to wire 2 and the other device wire to pin 5. Thinking of it as peeking on the electrical signal. Incidently, the actual telephones are connected in parallel.

Optimal Locations for a Telephone Tap

The diagram below shows the layout of a typical phone line installation at a domestic residence. The telephone line from the exchange comes into the property into a master socket. This master socket is typically in the hallway or lounge, but will of course vary from house to house. The extension sockets can be anywhere in the house and are usually connected to the master socket.

You’ll see 3 points that are marked on the diagram. Point 1 is between the master socket and the incoming telephone line from the exchange. Point 2 is between the master socket and extension socket A. Point 3 is between the master socket and extension socket B.

Here’s the key point; since the series and parallel devices are connected differently, they are capable of intercepting different telephones. The tricky one to understand is the series device, which is also the most common device.

Series telephone bugs will intercept all telephone conversations that are ‘downstream‘ of the bug. Using this concept, the incoming telephone line from the exchange is the top of the stream, and the extensions are the bottom of the stream. So the series bug will always go somewhere between the incoming telephone line and the target telephone. For example, placing the series bug at:

• Point 1 – intercepts telephones at Master Socket, Extension A and Extension B.
• Point 2 – intercepts telephones at Extension A only.
• Point 3 – intercepts telephones at Extension B only.

Since the electrical signal flows through a series device, if the phone at the master socket is used, but the series device is at point 2, then the electrical signal doesn’t reach the telephone tap. This is why the device placed at point 2 cannot intercept telephones at the master socket or extension B.

So the series telephone tap can target a specific phone (e.g. an office phone) or all of the phones in the house.

In contrast, a parallel telephone tap will intercept every telephone on the telephone line, regardless of where it is placed. For example, a parallel bug at:

• Point 1 – intercepts telephones at Master Socket, Extension A and Extension B.
• Point 2 – intercepts telephones at Master Socket, Extension A and Extension B.
• Point 3 – intercepts telephones at Master Socket, Extension A and Extension B.

And its as simple as that! Series and parallel telephone taps are installed differently, which mean they can target different telephones on the same telephone line. A parallel tap can intercept all telephones, and a series can target a specific telephone extension, or the whole line. So that concludes the technical article about telephone taps. I hope you enjoyed it!