A pressure sensor is provided, the sensor comprising an inlet for connecting to a body of gas； a diaphragm assembly comprising a first diaphragm and a second diaphragm, the first and second diaphragms defining a chamber therebetween, the chamber being connected to the inlet； a first transducer responsive to movement of the first diaphragm and operable to produce a first electrical signal in response to the same； and a second transducer responsive to movement of the second diaphragm and operable to produce a second electrical signal in response to the same； and an amplifier disposed in the chamber of the diaphragm assembly and connected to the first and second transducers to receive the first and second electrical signals therefrom. A movement sensor assembly for detecting movement of a person is also provided, the assembly comprising a flexible vessel containing a body of gas and a pressure sensor according to any preceding claim, the sensor being arranged to detect changes in the pressure of the gas within the flexible vessel.
