This is an equipment for the detection of eavesdropping devices on the telephone line.

Normally the telephone line-hooked listening devices are the most difficult to detect as these devices can be planted anywhere on the target line and majority of such installations will be outside the target premises and quite often some distance away.

Moreover, any professionally well made devices, though electrically connected to the telephone line, may not appreciably alter the electrical characteristics of the line, thus making its detection difficult. Also such devices are not easily recognizable in physical appearance.

Therefore using the instrument calls for good deal of expertise and knowledge of functioning characteristics of the telephone instrument and the telephone exchange of the locality. The currently available instruments can perform quick tests on single line and every wire combination of multiple lines also if needed.

Telephone bugs are planted for the purposes of listening to either the telephone conversation or the room conversations.