Abstract: A secrecy device connected between a telephone handset and a telephone body, which comprises a secrecy circuit for modulating a voice signal received from the handset on a predetermined modulation system basis to send a modulated voice signal to the telephone body and for demodulating a modulated voice signal received from the telephone body on a predetermined demodulation system basis to send a demodulated voice signal to the handset, and a detection circuit for detecting presence of a connection of a wiretapping telephone set to a line connecting two communicating party telephone sets.

Abstract: The device of the present invention discloses an electrical circuit which is electrically connected to a telephone line or data line between the telephone line or data line and the telephone set. In operation, the device continuously measures various electrical properties of the telephone or data line while a signal is passively generated on to the telephone or data line by simulating an on-hook to off-hook and back again condition of the telephone handset.

Abstract: A telephone privacy circuit is disclosed. The privacy circuit preferably includes a voltage breakdown device which passes current only when the voltage across the device is greater than a predetermined value. The voltage breakdown device is connected in series with a telephone to be protected. The predetermined value is chosen to be lower than the line voltage across the tip and ring terminals of a telephone line when every telephone connected to that line is in the on-hook position. In one embodiment of the invention, the predetermined value is selected to be higher than the line voltage across the tip and ring terminals of the telephone line when a telephone connected to that line is placed on the off-hook condition. In another embodiment of the invention, a voltage breakdown device is connected to the gating element of an electronic latching device.

Abstract: A method and system for detection of authorized connections to a telephone line where such connections are for the purposes of intercepting voice or data messages. The original or base line impedance would be measured by the system in response to the entry of a special code. The base line is stored in memory and used for subsequent impedance comparisons.

Abstract: Method and apparatus for detecting whether or not an unauthorized surveillance device has been installed on a communications line between user terminal equipment and central switching station equipment. Apparatus is installed at the central switching station and receives a test request signal from the user terminal equipment, such as a telephone. A receiving device receives the remotely generated test signal and activates the test. A measuring device then measures electrical characteristics of the communications line to determine the presence or absence of the "bug". The measuring device provides output signals indicative of the security status of the line. A signalling device responds to the output signals and provides a status signal to the user terminal equipment through the communications line. The status signal indicates the security status of the communications line.