<p>➀ LightLink is a novel system developed by the University of Calgary that enables full customization of commercial smartwatches using visible light communication between the display and external modules, bypassing traditional protocols like Bluetooth.</p><p>➁ The platform supports bidirectional data transfer, allowing third-party sensors (e.g., thermometers), actuators, and modules to be added without requiring firmware modifications or manufacturer support.</p><p>➂ Demonstrated with eight functional prototypes, LightLink empowers DIY developers and users to extend smartwatch capabilities, potentially fostering a low-cost ecosystem of modular light-based accessories.</p>