How Wiretapping Works

When you open up a phone, you can see that the technology inside is very simple. The simplicity of design makes the phone system vulnerable to surreptitious eavesdropping.

­­ Wiretapping occurs all the time in espionage and crime movies. Spies and gangsters know the enemy is listening, so they speak in code over the phone and keep an eye out for bugs. In the real world, we may not think much about wiretapping. Most of the time, we assume our phone lines are secure. And in most cases, they are, but only because nobody cares enough to listen in. If people did want to eavesdrop, they could tap into almost any phone line quite easily.

In this article, we'll explore the practice of wiretapping to see just how simple it is. We'll also look at a few different types of wiretaps, find out who taps phone lines and examine the laws that regulate this practice.


To learn how wiretapping works, you first have to understand the basics of telephones. If you take a look inside a telephone cord, you'll see how simple phone technology is. When you cut off the outer covering, you'll find two copper wires, one with a green covering and one with a red covering. These two wires make up much of the path between any two phones.

Inside a standard phone cord, you'll find a red wire and a green wire. These wires form a circuit like the one you might find in a flashlight. Just as in a flashlight, there is a negatively-charged end and a positively-charged end to the circuit. In a telephone cord, the green wire connects to the positive end and the red cord connects to the negative end.

The copper wires transmit the fluctuating sound waves of your voice as a fluctuating electrical current. The phone company sends this current through the wires, which are connected to the phone's speaker and microphone. When you speak into the receiver, the sound produces air-pressure fluctuations that move the microphone diaphragm back and forth. The microphone is hooked up so that it increases or decreases resistance (on the current running through the wire) in sync with the fluctuation in air pressure felt by the microphone diaphragm.

The varying current travels to the receiver in the phone on the other end and moves that phone's speaker driver. The heart of the driver is an electromagnet, which is attached to a diaphragm and suspended in front of a natural magnet. The wire carrying the varying electrical current winds around the electromagnet, giving it a magnetic field that repels it from the natural magnet. When the current voltage increases, the electromagnet's magnetism increases, and it pushes farther away from the natural magnet. When the voltage decreases, it slips back. In this way, the varying electrical current moves the speaker diaphragm back and forth, recreating the sound picked up by the microphone on the other end.

In its path through the global phone network, the electrical current is translated into digital information so that it can be sent quickly and efficiently over long distances. But ignoring this step in the process, you can think of the phone connection between you and a friend as one very long circuit that consists of a pair of copper wires and forms a loop. As with any circuit, you can hook up more loads (components powered by the circuit) anywhere along the line. This is what you're doing when you plug an extra phone into a jack in your house.

This is a very convenient system, because it's so easy to install and maintain. Unfortunately, it's also very easy to abuse. The circuit carrying your conversation runs out of your home, through your neighborhood and through several switching stations between you and the phone on the other end. At any point along this path, somebody can add a new load to the circuit board, in the same way you can plug a new appliance into an extension cord. In wiretapping, the load is a device that translates the electrical circuit back into the sound of your conversation.

This is all wiretapping is -- connecting a listening device to the circuit carrying information between phones. In the next few sections, we'll look at a few specific wiretaps and find out where they're connected to the circuit.



Basic Wiretapping Techniques

We've seen that tapping a wire is something like plugging an appliance into the electrical circuit running through your house. When you plug an appliance into the wall, the appliance draws power from the electrical current flowing in this circuit. The current in a phone line provides power as well, but it also carries information -- a pattern of current fluctuations that represents the air-pressure fluctuations of sound waves. A wiretap is a device that can interpret these patterns as sound.

One simple sort of wiretap is an ordinary telephone. In a way, you are tapping your own phone line whenever you hook up another phone in your house. This isn't considered wiretapping, of course, since there's nothing secretive about it.


Wiretappers do the same basic thing, but they try to hide the tap from the person they're spying on. The easiest way to do this is to attach the phone somewhere along the part of the line that runs outside the house. To configure a phone for tapping, the wiretapper just cuts one of the modular plugs (the part you insert in the jack) off a piece of phone cord so that the red and green wires are exposed. Then, the tapper plugs the other end of the wire into the phone and attaches the exposed wires to an accessible, exposed point on the outside phone line.

With this connection, the wiretapper can use the subject's line in all of the ways the subject uses it. The wiretapper can hear calls and make calls. Most wiretappers will disable the tap's microphone, however, so it works only as a listening device. Otherwise, the subject would hear the tapper's breathing and be alerted to the wiretap.

This sort of wiretap is easy to install, but it has some major drawbacks if you're a spy. First of all, a spy would have to know when the subject is going to use the phone so he or she could be there for the call. Second, a spy would have to stay with the wiretap in order to hear what's going on. Obviously, it's quite difficult to predict when somebody's going to pick up the phone, and hanging around a phone company utility box is not the most covert eavesdropping strategy.

For these reasons, spies will typically use more sophisticated wiretapping technology to eavesdrop on a subject. In the next section, we'll look at the main types of wiretapping equipment to see how spies listen in without blowing their cover.


Wiretapping: Bugs and Tape

Wiretapping equipment includes electronic bugs, voice-activated recorders and radio receivers. Learn about wiretapping equipment and electronic surveillance.

In the last section, we saw that the simplest wiretap is a standard telephone hooked into the wires of the outside phone line. The main problem with this system is that the spy has to stay with the phone in order to hear the subject's conversation. There are several tapping systems that get around this problem.

The simplest solution is to hook up some sort of recorder to the telephone line. This works just like your answering machine -- it receives the electrical signal from the phone line and encodes it as magnetic pulses on audio tape. A spy can do this fairly easily with an ordinary tape recorder and some creative wiring. The only problem here is that the spy has to keep the tape recording constantly to pick up any conversations. Since most cassettes only have 30 or 45 minutes of tape on either side, this solution isn't much better than the basic wiretap.


To make it functional, the spy needs a component that will start the recorder only when the subject picks up the phone. Voice-activated recorders, intended for dictation use, serve this function quite well. As soon as people start talking on the line, the recorder starts up. When the line is dead, it turns off again.

Even with this pick-up system, the tape will run out fairly quickly, so the spy will have to keep returning to the wiretap to replace the cassette. In order to stay concealed, spies need a way to access the recorded information from a remote location.

The solution is to install a bug. A bug is a device that receives audio information and broadcasts it through the air, usually via radio waves. Some bugs have tiny microphones that pick up sound waves directly. Just as in any microphone, this sound is represented by an electrical current. In a bug, the current runs to a radio transmitter, which transmits a signal that varies with the current. The spy sets up a nearby radio receiver that picks up this signal and sends it to a speaker or encodes it on a tape.

The bug picks up the electrical current that represents your conversation and broadcasts it to the spy's concealed receiving station.

A bug with a microphone can pick up any sound in a room, whether the person is talking on the phone or not. But a typical wiretapping bug doesn't need its own microphone, since the phone already has one. If the spy hooks the bug up anywhere along the phone line, it receives the electrical current directly. Often, the spy will hook the bug up to the wires that are actually inside the phone. Since people very rarely look inside their phones, this can be an excellent hiding spot. Of course, if somebody is searching for a wiretap, the spy will be uncovered very quickly.

This is the best sort of wiretap for most spies. Bugs are so small that the subject is unlikely to discover them, and once they are installed, the spy doesn't have to return to the scene of the crime to keep them running. All of the complicated recording equipment can be kept away from the phone lines, in a concealed location. But since the radio receiver has to be within range of the transmitter, the spy must find a concealed spot near the wiretap. The traditional receiving spot is a van parked outside the subject's home.

Of course, hanging out in a van and listening to someone's phone conversations is completely illegal for a civilian. But the law for the government is a little murkier. In the next section, we'll look at the history of government wiretapping and find out about the issues involved in wiretapping today.


Wiretapping Then and Now

Even in the earliest days of telephones and telegraphs, people were concerned about wiretapping. In the 1860s, before the modern telephone was even invented, many state courts in the United States enacted statutes that prohibited anybody from listening in on telegraph communication. By the 1890s, the modern telephone was in widespread use -- and so was wiretapping. From that time on, it has been illegal in the United States for an unauthorized person to listen in on somebody else's private phone conversation. In fact, it is even illegal to record your own phone conversation if the person on the other end is not aware that you're recording it.

Historically, the law has not been as strict for the government. In 1928, the United States Supreme Court approved the practice of wiretapping for the police and other government officials, though some states have banned it. In the 1960s and 1970s, this authority was curtailed somewhat. Law enforcement now needs a court order to listen in on private conversations, and this information can be used in court only in certain circumstances.


Additionally, the court order will only allow the authorities to listen in on a call for a certain length of time. Even under this tight control, the practice of government wiretapping is highly controversial. Civil-liberties advocates point out that when you tap a phone line, you are not only invading the subject's privacy, but also the privacy of the person the subject is talking to.

With the expansion of the Internet, many new concerns have come up. Modems use phone lines the same way traditional telephones do, but instead of transmitting a pattern of electricity that represents sounds, they transmit a pattern that represents the bits and bytes that make up Web pages and e-mail. The government (and others) can view this information using packet sniffers, such as the FBI's Carnivore system. Since it's not actually verbal conversation, Internet communication is not protected by the same laws that protect traditional phone use. But in 1986, the U.S. government enacted the Electronic Communications Privacy Act (ECPA), wiretapping regulation that protects e-mail, pagers and cell phone calls.

Many organizations, including the American Civil Liberties Union (ACLU), hold that the ECPA does not do enough to protect individual privacy. They charge that the act is not nearly as stringent as older wiretapping laws. Their primary arguments are that the authorities are allowed to monitor these communication lines in a much wider range of circumstances, and that there are too many judicial officials who can approve the wiretap. Also, only the content of the communication is afforded protection. The government is free to monitor who's communicating with whom, and how often.

Data encryption technologies are helping to curtail unauthorized wiretapping to some degree, but as encryption capabilities expand, so do wiretapping techniques. In the future, wiretapping probably won't be as easy as connecting a phone to the line outside somebody's house, but it will almost certainly continue in some form or another. Whenever information is transmitted from point to point, there is the possibility that a spy will intercept it along the way. This is nearly unavoidable in a global communications system.

To learn more about traditional wiretapping, modern wiretapping and the controversy surrounding government wiretapping, check out the links on the next page.