A system for monitoring a person may include a person-worn sensor device including at least one sensor (e.g., at least one accelerometer, magnetometer, altimeter, etc.) configured to collect sensor data and a processor to process data from the person-worn sensor device. The processor may be configured to determine or access an orientation of a physical support apparatus (e.g., bed, table, wheelchair, chair, sofa, or other structure for supporting the person), receive sensor data collected by the person-worn sensor device, calculate an orientation of the person relative to the physical support apparatus based on (a) the orientation of the physical support apparatus and (b) the sensor data collected by the person-worn sensor device, and identify, based on the determined orientation of the person relative to the physical support apparatus, a physical support apparatus exit condition indicating an occurrence or anticipated occurrence of the person exiting the physical support apparatus.