A battery-powered wearable sensor device , comprising: a sensor device body configured to be secured to a person or to an article worn by the person; a battery; a processor ; a data storage device , at least one sensor configured to generate sensor data regarding an orientation of the person; and an orientation display including a plurality of LEDs corresponding to a plurality of different orientations pressurizing a plurality of different body regions of the person; an orientation monitoring system wherein the processor is configured to monitor the orientation of the person over time in each of the plurality of different orientations pressurizing the plurality of different body regions based on the sensor data generated by the at least one sensor , including (a) determining a current orientation of the person and (b) monitoring and dynamically updating an accumulated amount of time spent in each of the plurality of different orientations; and a power savings control system wherein the processor is configured to: operate the wearable sensor device in a lower power mode in which the plurality of LEDs are maintained in an off state; detecting a predefined human input for waking the wearable sensor device and in response, automatically switching to an awakened mode; and in response to switching to the awakened mode, selectively activating a subset of the LEDs characterised in that the subset of the LEDs indicates both (a) the current orientation of the person, and (b) the accumulated amount of time spent in at least one of the plurality of different orientations. a sensor device body configured to be secured to a person or to an article worn by the person; a battery; a processor ; a data storage device , at least one sensor configured to generate sensor data regarding an orientation of the person; and an orientation display including a plurality of LEDs corresponding to a plurality of different orientations pressurizing a plurality of different body regions of the person; an orientation monitoring system wherein the processor is configured to monitor the orientation of the person over time in each of the plurality of different orientations pressurizing the plurality of different body regions based on the sensor data generated by the at least one sensor , including (a) determining a current orientation of the person and (b) monitoring and dynamically updating an accumulated amount of time spent in each of the plurality of different orientations; and a power savings control system wherein the processor is configured to: operate the wearable sensor device in a lower power mode in which the plurality of LEDs are maintained in an off state; detecting a predefined human input for waking the wearable sensor device and in response, automatically switching to an awakened mode; and in response to switching to the awakened mode, selectively activating a subset of the LEDs characterised in that the subset of the LEDs indicates both (a) the current orientation of the person, and (b) the accumulated amount of time spent in at least one of the plurality of different orientations. operate the wearable sensor device in a lower power mode in which the plurality of LEDs are maintained in an off state; detecting a predefined human input for waking the wearable sensor device and in response, automatically switching to an awakened mode; and in response to switching to the awakened mode, selectively activating a subset of the LEDs characterised in that the subset of the LEDs indicates both (a) the current orientation of the person, and (b) the accumulated amount of time spent in at least one of the plurality of different orientations. <EOS>