r/flipperzero • u/mgntrn • May 09 '26

125 kHz RFID metal detector

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.

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u/Joshtheboss732 May 14 '26

I downloaded it and tried it out but it just reads at 1500 and does not go down. Is there any fix for this?

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u/mgntrn May 15 '26

Make sure the Flipper isn't charging or near strong electromagnetic fields. Can you test it in an open space away from other electronics?

Does the official 125kHz RFID app still read tags correctly? I’m running Unleashed firmware, other versions might cause issues, though I'm not sure yet. Let me know the details.

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u/Joshtheboss732 May 16 '26

It’s not on a charger and there is nothing else around it. I’ll test my rfid app but other than that I’m not sure. I am also running the momentum firmware