A blood loss detection device for a hemodialysis system having a blood intake line, a dialysis machine including a pump, with the dialysis machine in communication with the blood intake line, and a blood return line in communication with the dialysis machine. The detection device includes a patch having an exterior edge and an opening through the patch forming a target for receipt of the return blood line. A slit through the patch extends between the exterior edge and the opening. A primary loop circuit terminates at two ends at the slit. An early warning alarm circuit loop terminates at two ends at the slit. An emergency shut-down circuit loop terminates at two ends at the slit. A modular connector connects the patch to an alarm activated by the early warning alarm circuit and to a switch mechanism activated by the shut-down circuit in order to shut down the dialysis machine and the pump.