An access disconnection system includes a blood treatment machine including a housing, an access site detection housing separate from the blood treatment machine housing, a transmitter positioned in the access site housing and configured to transmit an ultrasound wave into a blood stream of a patient, a receiver positioned in the access site housing and configured to receive a reflection of the ultrasound wave from the blood stream of the patient； and electronic circuitry in communication with the transmitter and the receiver. The electronic circuitry is supported by the access site detection housing, and the transmitter is configured to send a wireless disconnection output to the blood treatment machine. The disconnection output is indicative of a change in the reflected ultrasound wave received by the receiver sufficient to expect that an access disconnection of one of the arterial line and the venous line has occurred.
