A device (10) for detecting and showing a dangerous resistance to flow in a gaseous fluid through a filter (102). The device (10) is characterized: - by the fact that it comprises a body (11)； - by the fact that the body (11) is divided into two chambers (CH1, CH2) by an elastic membrane (MBN)； a preferably calibrated hole (13) connects the first chamber (CH1) with the patient end (A)； the second chamber (CH2) being in communication, instead, with the ventilator end (B), by means of a pressure-relief channel (14), which traverses the filter (102)； and - by the fact that it is provided with elements for detecting and showing a dangerous resistance to flow in a flow (FL) of gas that traverses the filter (102)； the detection elements comprising the membrane (MBN).
