RADD, the Reconnaissance and Detection Device Company, builds acoustic detection for unmanned aircraft. Its argument is that as drones shed their radio signatures through fiber control and onboard autonomy, sound becomes one of the few emissions left to detect. The Ground-based Lightweight Acoustic Dismounted Integrated UAS Sensor, GLADIUS, is carried by a dismounted team and alerts in real time as aircraft approach. The company says its technology comes out of operational experience with Tier 1 U.S. military teams.