While there is not much you can do about down-line taps, the Advanced Wiretap Detector will help you check your phone lines for on-premises series and parallel
bugs and wiretaps. You can also check your telephone for the most common types
of hookswitch bypasses. (A hookswitch bypass is a modification to the telephone
instrument that causes the transmitter or receiver in the telephone handset to
pick up room sounds and pass them down the phone line even with the phone hung
up. This effectively turns the telephone into a room monitor.)
The Advanced Wiretap Detector-46 detects series devices with a resistance
of 10 ohms or more. (Most series taps have a resistance of over 100
ohms.) It also detects parallel devices with a resistance of 65 megohms or
less. (Most parallel taps are under 30 megohms.) It can also detect certain
capacitively coupled taps.
Also included in the TT-46 is a line monitor that lets you
check the wire pairs for the presence of room audio when the phones are hung
up. (The presence of room audio on the phone line when the telephones
are not being used is a sure sign of bugging.) A line driver is part
of the monitor function. The line driver is used to turn on (activate) any
voltage operated microphones, such as FET mics, that may be connected to a pair
of wires.
Please note that neither the TT-46 or TT-07 are "magic boxes" that are connected permanently to a working phone line. They are both test sets that let you check your on-premises wiring and telephones for eavesdropping devices or taps. In order to do this, you must be able to disconnect your inside wiring from the telephone line coming into your home or business.
This is done at the interface between the telephone line and inside wiring; usually just by unplugging a cable at the interface box mounted on the side of the building. There is nothing difficult about this, but, of course, you must have access to this interface box.