A sterile device that includes a transducer intended to detect the movement of gases in a breathing circuit, and convert this into an electrical signal for relay to a ventilator (e.g., adult/paediatric/neonatal ventilators, anaesthesia system ventilators). It is connected to the breathing circuit and an appropriate data transfer cable and intended to enable the ventilator to display/monitor the gas flow to and from the patient, whereby controlled adjustments may be made. This is a single-patient device intended to be used for the duration of the treatment (single-use) before being discarded.