System and method for performing telephone line-in-use detection,

Abstract

A device connectable to a telephone line including detection circuitry for detecting telephone line events, such as telephone line-in-use, extension pick-up, and remote hang-up. The telephone line events are detected by monitoring the line voltage and loop current transmitted through the telephone line from a central office. A voltage sensor is connected to the telephone line to detect changes in the line voltage appearing in the telephone line. The changes detected in the line voltage are used in a line-in-use detection circuit to determine if the telephone line is already being used by another extension, while changes in loop current are used in a remote hang-up detection circuit to determine when a remote party ends their connection with the telephone line. An extension pick-up circuit is further provided for sensing changes in the telephone loop current in order to determine if a telephone extension has been picked up. If any of the circuits sense that one of these telephone conditions has occurred, the device may then change its mode of operation.