The Department of Defense, specifically the Army, is seeking innovative solutions for a Low-Altitude Passive Detection System aimed at enhancing the detection of small unmanned aerial systems (sUAS) operating at low altitudes. The objective is to develop a cost-effective, modular system capable of passive detection and identification of sUAS threats, providing a minimum notification time of three minutes from initial detection, and integrating seamlessly with existing Army systems. This initiative is crucial for improving advance warning capabilities for ground-based units against low-altitude threats, with potential applications extending to commercial sectors such as perimeter security and environmental monitoring. Interested parties can submit Direct to Phase II proposals for funding up to $2 million, with the application due by May 21, 2025. For further details, visit the solicitation link at https://www.dodsbirsttr.mil/topics-app/.