An access disconnection system includes: an arterial line; a venous line; a transmitter configured to transmit a sound wave in one of the arterial and venous lines when connected to a patient; a receiver configured to receive the sound wave from the other of the arterial and venous lines when connected to the patient; and electronic circuitry coupled to at least one of the transmitter and receiver, the circuitry configured to send a disconnection output indicative of a change in the sound waves received by the receiver from the transmitter sufficient to expect that an access disconnection of one of the arterial line and venous lines has occurred.