extremely low-frequency (ELF) magnetic field thrown off by its spinning brushless motors.

Now, researchers at Florida International University (FIU) have figured out how to use ELF to spot incoming threat drones

Typical active radar, optical, and acoustic systems face constraints from line-of-sight barriers, environmental background noise, and strict transmission regulations. Passive ELF magnetic sensing reduces these vulnerabilities by covertly capturing motor emissions. This technique operates silently, without broadcasting signals. It offers a stealthy detection alternative unaffected by weather conditions or acoustic interference.

“While the range of our method is limited for now, it costs only a few hundred dollars to develop and could run continuously without any specialized support, unlike radar systems,” Madanayake said.

The FIU team converts a basic physical requirement of drone flight into an effective security trap.

Although a 49 feet detection range remains modest, the system excels in its stealth and low manufacturing cost. A purely passive receiver emits no signals, making it invisible to hostile forces trying to jam or locate defensive sensors. Electromagnetic fields pass through fog, total darkness, and heavy environmental noise, providing reliable detection where optical and acoustic sensors routinely fail.

IDK, It sounds pretty impressive to me