A pressure sensor has an inlet 14 connecting to a body of gas, first and second brass diaphragms 6, 8, and cylindrical housing 10 defining a chamber. First and second piezoceramic transducers 20, 22 are connected to each diaphragm and amplifier 24 on circuit board 26 within the chamber. Lead 34 carries an electrical signal output from the amplifier. This is used in a movement sensor assembly for detecting movement of a personc, comprising a flexible vessel (204) such as a pad, mattress, pillow or cushion, containing a body of gas and the pressure sensor detecting changes in gas pressure within the vessel.
