Network security system for detecting removal of electronic equipment

A security system for detecting unauthorized disconnection of electronic equipment that is connected to a network communication link having existing pairs of data communication lines interconnecting said electronic equipment to a network, said system comprising:

• current loop means including separate current loops associated with different pieces of protected equipment and internally coupled to the associated pieces of protected equipment, each of said current loops using said existing pair of data communication lines which are coupled together via existing internal circuitry within said associated equipment to form a complete circuit path therethrough, and wherein respective pairs of data communication lines are associated with different ones of the associated pieces of equipment;
• source means for supplying a low DC current signal to each of said current loops;
• sensing means for sensing current flow through each of said current loops and detecting a change in said current flow through one of said current loops which is indicative of disconnection of one of the associated pieces of equipment;
• and
• output means for providing an alarm output signal so as to indicate detection of a disconnected one of said pieces of equipment.

A method for detecting unauthorized disconnection of remotely located electronic equipment which has existing data communication lines connecting the equipment to a network, said method comprising:

• selecting respective pairs of the existing data communication lines for associated pieces of monitored equipment so that each of said selected pairs of data communication lines forms a current loop through the associated pieces of monitored equipment, wherein said respective pairs of data communication lines are associated with different ones of the associated pieces of equipment;
• supplying a low DC current signal to each current loop so as to achieve continuous current flow through each current loop while each of said associated pieces of equipment is physically connected to said network via the data communication lines;
• and
• sensing said DC current signal in each of said current loops so as to detect a change in current flow indicative of disconnection of one of said pieces of associated equipment.