This $499 Open-Source Radio Can See WiFi Through Walls and Track Drones

The QuadRF, a handheld phased-array radio built on a Raspberry Pi 5 and FPGA, brings military-grade RF sensing to the open-source community — and it just hit #1 on Hacker News.

An open-source handheld device that can visualize WiFi signals through walls and track drones in flight has captured the top spot on Hacker News today. The QuadRF, built by ScaleRF, combines a Raspberry Pi 5 with a custom FPGA board capable of picosecond-level timing for advanced signal processing and beamforming.

Jeff Geerling, the hardware reviewer known for his exhaustive Raspberry Pi testing, got his hands on a prototype and was blown away by how well it works. The device operates in the 4.9–6 GHz range, covering the C-band used by WiFi 6E and many drone control links. It renders an augmented reality overlay that visualizes radio frequencies as colored blobs on your phone screen.

The privacy implications are hard to ignore. Geerling demonstrated the QuadRF spotting his neighbors' WiFi networks through walls by their unique frequency signatures, and tracking his father's DJI Mini Pro 4 in real time as it flew behind their studio. "If the open source community can come up with something like this, just imagine what governments are capable of," he wrote.

The QuadRF emerged from a larger project to build a Moon-scale antenna array for Earth-Moon-Earth radio experiments and radio astronomy, led by Martin McCormick — a former SpaceX engineer who worked on the Starlink terminal team. The handheld version is a scaled-down derivative, now available for pre-order on Crowd Supply starting at $499, with a Mobile Expansion Pack that adds battery power and a phone mount for portable RF scanning.

The project was first covered by Hackaday in June, but Geerling's hands-on review — demonstrating the device's practical ability to pierce walls and track drones in the field — has pushed it to the HN front page with over 270 upvotes.

Sources: Jeff Geerling, Hackaday, Crowd Supply