A mattress system comprising a plurality of interconnected chambers 16 and a control unit 14 connected to the chambers 16 and arranged to increase or decrease the pressure in the chambers 16 wherein the control unit has a sensor to detect the pressure in the chambers 16 and the control unit 14 can change from an active mode wherein it increases or decreases the pressure in the chambers 16 and a passive mode wherein it monitors the pressure in the chambers 16 depending on the pressure changes detected by the sensor. A calibration mode which measures weight based on a deflation time may be employed. The pressure readings may activate an alarm to indicate there is a risk of an ulcer developing. The device may measure whether a patient is moving sufficiently to avoid ulcers and may activate an alternating pattern of inflation. A pressure sensor mat may be used.
