Techniques are disclosed for monitoring the flow of blood returning to a patient from an extracorporeal therapy machine, such as a hemodialysis machine or an apheresis machine. Blood returning from such a machine is pumped, typically by a peristaltic pump, which returns the blood in pulsed flow or pulses. This flow can be sensed by Doppler flow sensors or accelerometers as it returns to the patient. If the flow is interrupted by dislodgement of the venous access needle, or by leaking of blood from the needle, these sensors will detect significantly different flow or vibrations. A controller can then cease therapy, alert a caregiver, or sound an alarm.
