An extracorporeal blood system comprising: a dialysis machine including an extracorporeal blood circuit; a vascular access enabling the extracorporeal blood circuit to be connected to a patient; first and second electrical contact coupling devices for connecting respectively to first and second lines (14, 16) of the extracorporeal circuit, the first and second electrical contact coupling devices including: first and second electrodes in electrical communication with the extracorporeal circuit such that the electrodes contact blood flowing through the extracorporeal blood circuit; and an electronics device; characterised in that: the system comprises first and second conductive contact members each configured to contact at least a portion of a surface of each of the first and second electrodes to place the first and second electrodes, respectively, into electrical communication with the extracorporeal circuit; and wherein the electronics device is connected to the conductive contact members for injecting an electrical signal into the extracorporeal blood circuit, the signal used to monitor the vascular access. a dialysis machine including an extracorporeal blood circuit; a vascular access enabling the extracorporeal blood circuit to be connected to a patient; first and second electrical contact coupling devices for connecting respectively to first and second lines (14, 16) of the extracorporeal circuit, the first and second electrical contact coupling devices including: first and second electrodes in electrical communication with the extracorporeal circuit such that the electrodes contact blood flowing through the extracorporeal blood circuit; and an electronics device; characterised in that: the system comprises first and second conductive contact members each configured to contact at least a portion of a surface of each of the first and second electrodes to place the first and second electrodes, respectively, into electrical communication with the extracorporeal circuit; and wherein the electronics device is connected to the conductive contact members for injecting an electrical signal into the extracorporeal blood circuit, the signal used to monitor the vascular access. first and second electrodes in electrical communication with the extracorporeal circuit such that the electrodes contact blood flowing through the extracorporeal blood circuit; and an electronics device; characterised in that: the system comprises first and second conductive contact members each configured to contact at least a portion of a surface of each of the first and second electrodes to place the first and second electrodes, respectively, into electrical communication with the extracorporeal circuit; and wherein the electronics device is connected to the conductive contact members for injecting an electrical signal into the extracorporeal blood circuit, the signal used to monitor the vascular access. the system comprises first and second conductive contact members each configured to contact at least a portion of a surface of each of the first and second electrodes to place the first and second electrodes, respectively, into electrical communication with the extracorporeal circuit; and wherein the electronics device is connected to the conductive contact members for injecting an electrical signal into the extracorporeal blood circuit, the signal used to monitor the vascular access.