A German system tracks hidden drones by listening to their engines

A drone slips behind a building and vanishes from a camera’s view. Fog closes in. Radar and optical sensors lose a clean line of sight. The machine is still there, though—and Fraunhofer IDMT has built a system that listens for it, identifying the sound of its motors and rotors and tracking its position in real time.

The technology was developed by the institute’s Oldenburg branch. Its microphones capture the acoustic fingerprint of a drone, while machine-learning algorithms distinguish that pattern from the surrounding noise. Multiple microphones add directional information, allowing the system to determine where the sound is coming from and locate the drone in space.

That makes acoustics useful in the places where visual and radio-based sensors struggle: built-up areas, forests, terrain-obstructed sites and poor weather. The sensor is passive—it receives sound and vibration without transmitting a signal of its own—so it can run autonomously with minimal power draw and remain undetectable. Christian Rollwage, the group manager, said the acoustic approach offers a cost-effective, low-maintenance complement to existing detection systems.

And concretely? Security teams could use the acoustic signal as an early warning, then wake cameras or radar only when a drone appears nearby. That could add coverage without asking one sensor to solve every visibility problem. The approach is aimed at airports, critical infrastructure, military sites and large public events, where a drone beyond line of sight is hardest to detect.

Fraunhofer IDMT has been working on acoustic drone detection and localization since 2016, through joint projects including AMBOS and ALADDIN. The result now exists as standalone software components and a fully integrated system. It will be demonstrated live inside the mobile platform nicknamed The Hearing Car at Drone Days 2026 in Bremen and Hatten, Germany, on August 27 and 28. The broader idea could eventually be applied to other distinctive sounds, including vehicle engines or gunshots, but the current demonstration is focused on drones.