I study how security breaks across the global AIoT supply chain, from white-label manufacturing to cross-border marketplaces that distribute insecure, increasingly AI-enabled devices at scale. My work focuses on safeguarding vulnerable user groups, including households and children, whose devices often inherit systemic weaknesses from opaque upstream vendors. I combine Internet-wide measurements, device and firmware reverse engineering, and machine learning to uncover structural risks, and to examine how AI is reshaping both the threats to and the defenses available for connected ecosystems.