The Duolingo English Test (DET) mobile app acts as a secure companion utility for the Duolingo English Test certification platform, facilitating remote proctoring, ID verification, and environment scanning. It is designed for international students and professionals who require a flexible, on-demand alternative to traditional, appointment-based English proficiency testing. By leveraging the mobile device as a secondary security camera and verification tool, the app enables a rigorous, proctored testing experience that can be completed from anywhere. This positions the service as a highly accessible and cost-effective solution in the competitive landscape of global academic and professional certification.