Abstract: A differential pressure indicator including a remote sensing means is disclosed wherein a reference volume under predetermined pressure is employed as a standard, triggering an indicating mechanism when a second (measured) pressure falls above or below a predetermined threshold. The indicating mechanism may include a novel shaft which protrudes through the casing carrying thereon a source of radioactive material which is remotely monitored. Alternatively, the protrusion may be sensed as an impedance variation or additional visual indicator. In one embodiment, a plurality of the subject sensors are housed upon the blades of a helicopter. Upon sensing the changing pressure in the helicopter blade, the protruding element provides a radioactive source which is sensed in a conventional manner to provide a cockpit readout.