Abstract: A receiver is disclosed connected to a McCulloh loop, having an N or line side and a G or ground side, for receiving coded alarm signals from a plurality of McCulloh transmitters. The receiver is especially adapted for supplying the alarm signals to a computer and has N and G process logic circuits to ensure that the polarity of the output signals supplied to the computer from the logic circuits remains the same regardless of the polarity of input signals supplied to the logic circuits. The receiver also has an inhibit circuit to prevent the G process logic circuit from supplying its output to the computer except upon the occurrence of a fault condition in the McCulloh loop, a fault sensing circuit for sensing a fault in the McCulloh loop and for connecting the ground side of the loop and the line side of the loop together and a sampling circuit for testing the McCulloh loop during a fault condition to resume normal operation in the loop upon the clearance of the fault.