System for and method of indicating intruder presence on telephone lines, and method of installation of telephone intruder alarm system

A compact telephone intruder alarm system for indicating the subsequent interconnection and disconnection of an extension telephone with a telephone line to a current on-line user, comprising:

• (a) means for detecting electrical OFF- and ON-hook signals which are respectively generated in response to interconnection and disconnection of an auxiliary extension telephone with a telephone line, said detecting means including a rectifier sub-circuit for rectifying the electrical hook signals to thereby substantially eliminate undesirable voltage variations on the electrical hook signals;
• (b) means responsive to the detection of the electrical OFF- and ON-hook signals 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 the auxiliary extension telephone, to thereby alert the on-line user to the presence of an intruder on the telephone line;
• and
• (c) means for mounting both said detecting means and said indicating means on the primary extension telephone, to thereby simplify installation of the compact telephone intruder alarm system with conventional telephones.

A compact telephone intruder alarm system for indicating the subsequent interconnection and disconnection of an extension telephone with a telephone line to a current on-line user, comprising:

• (a) means for detecting electrical OFF- and ON-hook signals which are respectively generated in response to interconnection and disconnection of an auxiliary extension telephone with a telephone line;
• (b) means responsive to the detection of the electrical OFF- and ON-hook signals 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 the auxiliary extension telephone, to thereby alert the on-line user to the presence of an intruder on the telephone line;
• (c) means for mounting both said detecting means and said indicating means on the primary extension telephone, to thereby simplify installation of the compact telephone intruder alarm system with conventional telephones;
• (d) said electrical OFF-hook signal having a voltage versus time characteristic whose amplitude drops from a predetermined DC voltage level before said interconnection is made, to a lower DC voltage level after, and for as long as, such interconnection;
• said electrical ON-hook signal having a voltage versus time characteristic whose amplitude rises from the lower DC voltage level before said disconnection is made, to the predetermined DC voltage level after such disconnection;
• said detecting means being operative for sensing the changes in voltage level of said signals;
• said indicating means being operative for continuously indicating the presence of the intruder on the telephone line all during the time that the lower DC voltage level is present on the telephone line;
• and
• (e) said indicating means including a current-actuatable indicator which is actuatable from a non-alarm state to an alarm state in response to passage of an electrical current of a predetermined magnitude through the indicator;
• said detecting means including a power source for generating current, pre-set means electrically connected to both the power source and the telephone line for adjustably setting the current passing through the indicator to a current-balanced equilibrium position at which electrical current from both the power source and the telephone line has a reduced magnitude which is slightly less than said predetermined magnitude, and means for amplifying the detected electrical OFF-hook signal from said reduced magnitude to a magnitude which is at least equal to said predetermined magnitude to thereby indicate the start of the interconnection of the auxiliary extension telephone.

A method of installing on a conventional telephone network a compact telephone intruder alarm system of the type including:

• (A) means for detecting electrical OFF- and ON-hook signals which are respectively generated in response to interconnection and disconnection of an auxiliary extension telephone with a telephone line;
• and
• (B) means responsive to the detection of the electrical OFF- and ON-hook signals 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 the auxiliary extension telephone, to thereby alert the on-line user to the presence of an intruder on the telephone line;
• said method of installation comprising the steps of:
• (a) mounting the detecting means on the primary extension telephone;
• (b) mounting the indicating means on the primary extension telephone;
• (c) both of said mounting steps being performed by mounting the detecting means and the indicating means within the interior of the handset of the primary extension telephone to thereby make the installation of the compact alarm system with conventional telephones hardly discernible;
• and
• (d) both of said mounting steps being simultaneously performed by first removing the conventional receiver cover from the handset, and thereupon replacing the conventional cover with a modified receiver cover in which both the detecting means and the indicating means are mounted.

A compact telephone intruder alarm system for indicating the subsequent interconnection and disconnection of an extension telephone with a telephone line to a current on-line user, comprising:

• (a) multi-component means for detecting electrical OFF- and ON-hook signals which are respectively generated in response to interconnection and disconnection of an auxiliary extension telephone with a telephone line;
• (b) multi-component means responsive to the detection of the electrical OFF- and ON-hook signals 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 the auxiliary extension telephone, to thereby alert the on-line user to the presence of an intruder on the telephone line;
• (c) a transmitter cover mounted on the handset of the primary extension telephone and bounding an interior transmitter compartment therewith in which a microphone transmitter is mounted;
• (d) all of the components of said multi-component detecting means and said multi-component indicating means being of a miniature size sufficient to be received with clearance in the interior transmitter compartment;
• and
• (e) means for mounting all of the miniature components of said detecting means and said indicating means within the interior transmitter compartment of the handset of the primary extension telephone, to thereby make the installation of the compact telephone intruder alarm system with conventional telephones hardly discernible.

A method of indicating the subsequent interconnection and disconnection of an extension telephone with a telephone line to a current on-line user, comprising the steps of:

• (a) providing a current-actuatable indicator which is actuatable from a non-alarm state to an alarm state in response to passage of an electrical current of a predetermined magnitude through the indicator;
• (b) supplying current to the indicator;
• (c) adjustably pre-setting the current passing through the indicator to a current-balanced equilibrium condition in which the current passing through the indicator has a reduced magnitude which is slightly less than said predetermined magnitude;
• (d) detecting electrical OFF- and ON-hook signals which are respectively generated in response to interconnection and disconnection of an auxiliary extension telephone with a telephone line;
• (e) amplifying the detected electrical OFF-hook signal from said reduced magnitude to a magnitude which is at least equal to said predetermined magnitude;
• and
• (f) indicating in response to the detection of the amplified electrical OFF-hook signal and to the respective detection of the electrical ON-hook signal to a current on-line user of a primary extension telephone which is already interconnected with the telephone line of the subsequent interconnection and of the respective disconnection of the auxiliary extension telephone, to thereby alert the on-line user to the presence of an intruder on the telephone line.

A method of installing on a conventional telephone network a compact telephone intruder alarm system of the type including:

• (A) multi-component means for detetecting electrical OFF- and ON-hook signals which are respectively generated in response to interconnection and disconnection of an auxiliary extension telephone with a telephone line;
• (B) multi-component means responsive to the detection of the electrical OFF- and ON-hook signals for indicating to a current on-line user of a primary extension telephone which is already interconnected with the telephone line of the subsequent internconnection and disconnection of the auxiliary extension telephone, to thereby alert the on-line user to the presence of an intruder on the telephone line;
• and
• (C) all of the components of said multi-component detecting means and said multi-component indicating means being of a miniature size sufficient to be received with clearance in the interior transmitter compartment of the handset of the primary extension telephone;
• said method of installation comprising the steps of:
• (a) mounting the miniature components of the detecting means within the interior transmitter compartment of the handset of the primary extension telephone;
• and
• (b) mounting the miniature components of the indicating means within the interior transmitter compartment of the handset of the primary extension telephone, whereby installation of the compact telephone intruder alarm system with conventional telephones is simplified and made hardly discernible.