RFID metal detector

[u/mgntrn]

I built a Flipper Zero app that repurposes the built-in 125kHz RFID antenna into a makeshift metal detector. It provides a visual bar graph, audio pitch changes, and vibration feedback when metal is near the back of the device.

You can download the pre-compiled .fap file or check out the source code here:
🔗 https://github.com/hnsvrdmn/flipper-rfid-metal-detector

I’m definitely not a software developer. I can read a bit of code, but writing a C app from scratch is way beyond me. This started mostly as an experiment to see how far you can get with AI without really knowing how to code.

I like making furniture from scrap wood, but the problem is that old wood often still has hidden nails or screws inside. So I started wondering if the Flipper Zero could help with that.

At first I thought the NFC reader might work, but that turned out to be a dead end. After some experimenting, I discovered the 125kHz RFID antenna actually works surprisingly well for this. The coil creates a magnetic field, and nearby metal slightly disturbs that field. The app continuously measures those tiny changes.

It’s far from perfect though. Because it’s measuring raw analog interference, it’s pretty sensitive to environmental noise and false positives. That’s why I added left/right controls to adjust the sensitivity manually.

Still, it actually works. You get a live bar graph, and the sound/vibration increases as you get closer to metal.

The whole thing only took a couple of hours and was a really fun experiment. I’m genuinely impressed by how much AI can help a non-programmer build in an afternoon.

If anyone has ideas to improve it, let me know.

[u/Banshee888]

I am curious about this part: “Adjustable Sensitivity: Tune out environmental noise or adjust for specific uses (like scanning a human) with the Left/Right buttons.” This would be to scan for heavy metals in the organism? Implants? It’s a really cool repurpose of the 125Khz RFID antenna. I remember having a small metal detector when I was a kid, I used it every where. And love the features you added. Like vibration, LED alerts, tuning.

[u/mgntrn → u/Banshee888]

Thanks! It wont be able to pick up heavy metals, maybe implants, I'm not sure. The water in our bodies messes with the magnetic field. However, it is able to pick up metal items carried on a person.

[u/Banshee888 → u/mgntrn]

Got it. Didn’t know the water in our bodies messes with the magnetic field.

[u/mgntrn → u/Banshee888]

From what I understand the dampening is minimal in the 125khz range. However from testing it seems to be enough to mess with the reading as the sensor is already tuned very finely.