Abstract: A system is provided for electronically monitoring a group of sensor switches employed at remote locations in security or alarm systems. To monitor the status of individual switches, a matrix of conductors is employed. The matrix has a predetermined number of send conductors by a predetermined number of return conductors. Switch circuits each having a diode connected in series with one of the sensor switches are connected at selected crosspoints of the matrix of conductors between respective send and return conductors. Line selection circuitry responsive to an input signal from a computer selectively permits the supply of a sourcing voltage potential to at least a selected one of the send and return conductors and the supply of a sinking voltage potential to at least a selected one of the remaining send and return conductors.