Abstract: A system, methods, and apparatus having a circular buffer for the reply of renal therapy machine alarms and events are disclosed. An example renal therapy apparatus includes a therapy operations processor configured to generate alarms, events, and high fidelity medical device data. The renal therapy apparatus also includes a memory device having a circular buffer configured to store a duration of medical device data. The renal therapy apparatus further includes a control processor configured to receive a stream of medical device data from the therapy operations processor, and write the stream to the circular buffer such that a most recent duration of the stream is stored. The control processor is also configured to detect an occurrence of an alarm or event, and create a reply record that includes an identifier of the alarm or event and the medical device data that is stored in the circular buffer.