An extracorporeal blood system includes: (i) an extracorporeal blood machine; an extracorporeal blood circuit coupled operably to the machine, the extracorporeal blood circuit including first and second blood lines, the blood lines configured to be in blood flow communication with a patient; (ii) an electrical loop including first and second electrodes placed in contact with blood flowing through the extracorporeal blood circuit; (iii) a device configured to inject an electrical signal into the blood circuit via the loop; and (iv) a third electrode placed in contact with blood flowing through the extracorporeal blood circuit, the third electrode configured to enable a change in an electrical value to be measured so that an access disconnection of the extracorporeal blood circuit from the patient can be measured.