Peripheral device for head-mounted display

A head-mounted display (HMD) system, comprising:

• a HMD device comprising a camera;
• and
• a peripheral device dockable to the HMD device, the peripheral device comprising:
• a plurality of light source elements disposed along a perimeter of a face of the peripheral device;
• and
• a peripheral electronic control system comprising instructions that, when executed by one or more processors of the peripheral electronic control system, cause the peripheral electronic control system to perform operations comprising:
• forming an optically detectable light pattern with the plurality of light source elements by controlling each of the light source elements, the HMD device being configured to detect the optically detectable light pattern with the camera and to display an augmented reality (AR) content based on the identified optically detectable light pattern.