Telephone intruder alert system

Abstract

A telephone intruder alert system is operative for indicating to a current on-line user of a primary extension telephone which is already interconnected with the telephone line of the subsequent interconnection and disconnection of another auxiliary extension telephone with the same telephone line. Electrical click signals of limited time duration are generated each time an extension telephone is interconnected or disconnected with the telephone line, and each click signal is successively detected, filtered and electrically amplified before being conducted to a relay alarm circuit. The first detected click signal indicates the start of the interconnection of the auxiliary extension telephone, and the second detected click signal indicates the end of this interconnection. A timing arrangement energizes and deenergizes the alarm circuit prior to the end of the duration of the first and the second click signals, respectively. A switch selectively disables the intruder alert system.