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Audio surveillance equipment

Audio surveillance equipment

Audio surveillance equipment is used for a huge number of reasons by all sorts of eavesdroppers from the amateur looking for voyeuristic thrills to government law enforcement agencies tracking criminals.

Audio surveillance is even used by employers for training purposes and to monitor employee's telephone usage, ensuring that they are not using company telephones for personal calls. It is also commonly used in large corporations to make sure employees are not leaking sensitive information or illegally obtaining sensitive information from competitors.


Top audio surveillance equipment: wireless device systems

Audio surveillance can take place in the form of 'bugging' or wiretapping. Wiretapping is a way of eavesdropping by connecting to a channel of communication, such as a telephone. A bug is a listening device that does not need to be physically connected to any communications medium to eavesdrop as they use wireless transmission technology.


Wiretapping is typically used for secretly listening in on telephone conversations and can be done in using the following methods and devices:

Telephones - the cheapest and most basic form of phone tapping is similar to hooking another phone up to an existing phone line. However, instead of plugging the phone in at the jack it is connected at another accessible point along the line (usually a phone company utility box) using exposed wires. This is not practical because an eavesdropper would need to know when the phone is going to be used in order to know when to listen in; and someone sitting near a phone utility box all day is likely to look suspicious.

Recorders - another more practical and popular way to tap a phone is to use a recorder hooked up to the telephone system instead of another telephone. This way conversations can be recorded and listened to later eliminating the risk of being seen sitting at a utility box. Recorders receive electrical signals from the phone line and record them onto an audio tape. Ordinary recorders record continuously which is a waste of tape unless a telephone conversation lasts from the moment recording starts till the end of the tape.

Voice-activated recorders - these can be used to save memory space because they only start recording when someone speaks and stops recording when the line goes dead. The problem is that tapes can usually only hold up 40 minutes of recording on either side so even with voice-activated recorders the tape will need to be turned and changed quite regularly.


Bugs have become the top choice for audio surveillance equipment of all descriptions from phone tapping to catching radio signals from a computer monitor. Bugs have become popular because they combine small size with the ability to transmit audio information through the air. Some use microphones to pick up sound waves but most bugs use radio frequency.

A bug can be connected to a phone anywhere along the line but they are typically placed in the telephone receiver. As most people tend to presume their phone lines are secure and rarely even consider the fact their phone may be tapped, it is a pretty good hiding place. However, if someone were searching for bugs, the receiver is the first place they would look. Bugs can also be hidden in small everyday items such as a pen, shirt button or a calculator. Bugs that are not connected to a phone require microphones in order pick up any sound.

The biggest advantage to the bug is the fact that once it is installed all sound can be listened to and recorded remotely from a hidden location. However, the drawback is that because they are wireless, the signal receiver needs to be fairly near to the transmitter. In some cases this means the hidden location may not be as concealed as it should be. A good example of such a location is a van parked outside a house.

Audio surveillance can be difficult to detect. See the counter surveillance page for further information.