A patient support (10, 14) comprising: a source of pressurized air; a first bladder; a valve in fluid communication with the source of pressurized air and with the first bladder and configured to control the flow of air between the source of pressurized air and the first bladder; a first pressure sensor in fluid communication with the first bladder and producing a first pressure signal indicative of air pressure within the first bladder; a controller in electrical communication with the source of pressurized air, valve, and first pressure sensor, the controller comprising (i) a processor, and (ii) a memory device electrically coupled to the processor, the memory device having stored therein a plurality of instructions which, when executed by the processor, cause the processor to: determine a position of the patient supported on the first bladder, monitor the first pressure signal to determine a rate of change of pressure in the first bladder by comparing the change from a first pressure to a second pressure over a known time interval, and determine whether the patient has changed positions on the first bladder by determining if the rate of change of pressure is greater or less than a threshold value; and a weight sensor in electrical communication with the processor to input a signal to the processor indicative of at least a portion of the weight of the patient supported on the patient support (10, 14) and the threshold value is a function of the patient weight. a source of pressurized air; a first bladder; a valve in fluid communication with the source of pressurized air and with the first bladder and configured to control the flow of air between the source of pressurized air and the first bladder; a first pressure sensor in fluid communication with the first bladder and producing a first pressure signal indicative of air pressure within the first bladder; a controller in electrical communication with the source of pressurized air, valve, and first pressure sensor, the controller comprising (i) a processor, and (ii) a memory device electrically coupled to the processor, the memory device having stored therein a plurality of instructions which, when executed by the processor, cause the processor to: determine a position of the patient supported on the first bladder, monitor the first pressure signal to determine a rate of change of pressure in the first bladder by comparing the change from a first pressure to a second pressure over a known time interval, and determine whether the patient has changed positions on the first bladder by determining if the rate of change of pressure is greater or less than a threshold value; and determine a position of the patient supported on the first bladder, monitor the first pressure signal to determine a rate of change of pressure in the first bladder by comparing the change from a first pressure to a second pressure over a known time interval, and determine whether the patient has changed positions on the first bladder by determining if the rate of change of pressure is greater or less than a threshold value; and a weight sensor in electrical communication with the processor to input a signal to the processor indicative of at least a portion of the weight of the patient supported on the patient support (10, 14) and the threshold value is a function of the patient weight.