A security system for detecting disconnection of electronic equipment from a network, said security system comprising: current loop means including separate current loops associated with different pieces of monitored equipment, each of said current loops employing a pair of data communication lines which connect one of the associated pieces of equipment to the network and which are coupled to existing internal circuitry within the associated piece of monitored equipment, 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; and detector means for monitoring the current signal through each of said current loops and detecting a change in said current signal through one of said current loops which represents disconnection of said associated piece of equipment from the network. view more