This innocuous looking box when attached to your phone is an innovative gizmo which can monitor the other party’s conversations. Say you are talking to somebody on the phone, but want to know what he is discussing with other people in the room. If the gadget is attached to your phone, you put the person on hold. This hold is not real, but the person thinks it is.

The hold invader thus acts like a room bug and you can hear whatever conversation or sounds are emanating from that end of the line. In order to get the best out of this gadget, you should start the conversation and while it is at an important juncture, interrupt and put the person on hold, saying you have to attend to an incoming call (it has a built-in incoming call simulator) and put him on hold.

While that person thinks the phone is on hold – and there is a dead sound on the phone – he may say something incriminating, or something which may be of use to you in some way. He won’t be able to hear anything you say at this point because your phone’s microphone will be cut off. When you get back to him, you will be in possession of important information and this can be of use to you in business negotiations or even on a personal level.

Originally designed for a federal investigative agency in the US, the hold invader is intended and sold only for legal and lawful use.

Those working in business sometimes worry their phone may be bugged because someone wants to hear what they are saying in order to steal information if they are a competitor, for example.

The practice of phone bugging is something the police employ quite regularly, but of course, in their case the bugging is done legitimately as they may wish top keep tabs on someone in a case they are following without their knowledge.

The device, called the RF detection telephone analyser, continously sweeps the phone for any unusual signs it may recieve which could indicate unusual activity on the phoneline such as bugging, which is indicated by an LED light. It works both when the phone is not in use but also when in use so you can tell if anyone is trying to listen into a converstation while speaking, in which case the idea would be to cease talking at once.

The device also looks for other RF signals so could pick up on other bugging activity that uses radio frequency.

People may want to keep record of incoming and outgoing calls for one reason or another. It might be for business or even as a security measure.

This device known as Teleport 2 can generate a log of all your calls and record it on your PC. Furthermore, it also records the actual calls in audio form. So anytime you need to refer back to any of the calls for any good reason, you can simply play back the audio of the call and hear at your leisure.

The device called Teleport 2 connects to the phone line and has an USB connection to hook up to the PC.

Its not a surveillance gadget in the real sense but can be used to that effect in some instances. For example, a telephone tap device such as this can also act as a security tool because if you happen to get threatening calls or the like, it enables you to save the number and the actual recording of the call as proof or evidence. It can also be used to monitor calls made by your teenage son or daughter so they don’t get into mischief and run up the phone bill. Then again, they will probably unhook the device before making their calls!

This is made to international standards and will work with most phones in the UK. More information on the product is available here.

This telephone number logger highlights a very different aspect of surveillance. Rather than listening to the calls themselves, this very small devices will log up to 2000 incoming and outgoing telephone numbers. The incoming telephone numbers are only recorded if a Caller ID service is available on the telephone line.

The design is very simple, and is not particularly geared towards surveillance. I can imagine that a parent would use this to monitor the telephone calls being made in a family, or even by individuals living at a shared property.

However, it doesn’t mean that a useful device cannot be used for surveillance. How many times do you see in the movies someone taking a glass up to a door? (Which does work by the way).

While looking around on MAKE Magazine, I found a useful little circuit for a telephone bug. I know how much you guys love circuit diagrams!

The bug is a serial device, which meals the phone connects to the bug, and then the bug connects to the telephone line. This means that only that particular phone is bugged. Potentially, you could build the bug into the phone itself.

The design is suited to the US phone network, not sure if it’d work in the UK. You can substitute 4 1N4148 Diodes for the IN4384 Diodes too.

In a recent article, I discussed the difference between parallel and series telephone taps. In this article, I present a very simple and reliable parallel phone tap circuit useful for recording telephone conversations onto a tape recorder.

When installing a telephone tap, its advisable not to cut the telephone line in anyway. Cutting the telephone line for any time is detectable, and therefore series devices can be detected in this way. Parallel devices can be installed without cutting any telephone wires, and is thus harder to detect.

The diagram shows a simple circuit using just 6 very cheap and common components. To build the circuit, you’ll need some Veroboard or prototype board (whatever you favourite is), some wire, and a 3.5mm plug that will connect to your tape recorder’s microphone input socket. I’ve left it to the reader to work this bit out, as its very simple to do but quite awkward to explain!

To test the circuit, connect the telephone line wires to pins 2 and 5 of the telephone line. Then plug the microphone input into your tape recorder. Pick up the telephone and press record on your tape recorder. You should be able to hear a dialtone on the tape when you play it back.

If you’re curious to what goes on in the circuit, I’ll explain that now. The resistors act as a potential divider, and limit the voltage from the phone line that reaches the recording device. The diodes ensure the incoming voltage is rectified from an alternating current (AC) to a direct current (DC), which might otherwise damage your tape recorder.

The capacitors should be a ceramic type, rated at 50V or more. The emphasis is that the capacitors should not be polarised, which would stop the circuit from working properly. The resistors can be 1/4 Watt carbon or metal film types. As you can see, the components are very cheap.

The circuit is designed to work on UK telephone lines. However it should work in other countries too. You may need to adjust the resistor values to get the best volume. To increase the volume to the tape recorder, increase the value of R2. If the sound on the tape recorder is distorted, then try decreasing the value of R2 to decrease the volume.

If your tape recorder has a voice activated system (VAS), then you can set your tape recorder to record whenever the phone is used. You just need to adjust the recording to trigger when the telephone handset is lifted.

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!