An exemplary non-invasive wearable brain interface system includes a headgear configured to be worn on a head of a user, a plurality of self-contained photodetector units configured to removably attach to the headgear, the photodetector units each comprising a plurality of photodetectors configured to detect photons of light after the photons reflect from a target within a brain of the use, and a master control unit coupled to each of the photodetector units and configured to control the photodetector units.