An extracorporeal blood system includes: an extracorporeal blood machine; an arterial line extending from the extracorporeal blood machine; a venous line extending from the extracorporeal blood machine; and an access disconnection circuit for detecting a disconnection of at least one of the arterial or venous lines from a patient, the access disconnection circuit including (i) a signal generation source having first and second signal generation source electrical lines each in electrical communication with blood traveling through one of the arterial or venous lines, (ii) a conductive pathway electrically communicating blood traveling through the arterial line with blood traveling through the venous line, and (iii) a signal processing unit positioned and arranged to process a signal generated by the source to detect the disconnection of the at least one of the arterial and venous lines.