01Silence
Drones can go radio‑silent. Rotors are never silent.
Most drones stay in touch with a pilot. Commands go up, video comes down, and radio sensors find the drone by listening in.
Newer drones cut that link. Some fly on a hair-thin fibre-optic cable. Others follow a route on their own. On the radio, there is nothing left to hear.
The rotors keep turning. To stay up, a drone has to beat the air, and every beat sends a ripple of pressure outward. That ripple is sound.
02Signature
A rotor hums in a pattern of its own.
Every time a blade sweeps past, it gives the air a small push. A small drone’s rotors do that hundreds of times a second.
The pushes come at a steady beat, so they add up to a hum: one low note, with higher notes ringing at two, three and four times its pitch.
Other sounds build their notes differently. EchoNet is trained to know a rotor’s.
03Movement
Several nodes hear the flight.
Nodes spread across the ground listen for the same rotor sound.
Each report shows which part of the ground heard it and when.
As the reports come in, the person on watch can follow the sound across the network.
04Network
A net across the ground.
EchoNet spreads small nodes across the ground you hold. Each one listens over its own patch and reports what it hears.
A radar has to send out a signal to see, and that signal can give it away. A node only has to listen.
Darkness takes away a day camera’s view. EchoNet keeps listening for rotors after the light is gone.
Each node listens on its own. Lose one, and the rest keep listening.
05Proof
See what raised the alert.
An alert shows which nodes heard rotor sound and when they reported it.
The person on watch can trace the alert back to those reports.
The record keeps them for later review.