How would one test this device to know that it works? It would seem actual cell site simulators would be rare in the wild for many HN readers.

You could bring it to a large festival or even a protest. Law enforcement deploys them all the time. I found one using SnoopSnitch on an Android phone while at a large festival here in Louisiana.

Does that work by comparing known cell sites to found cells sites? I know some StingRay detectors use that method and it's prone to false positives around large events where mobile carriers or 3rd parties bring in legitimate temporary cell sites to improve cell service at the venue and provide more capacity.

Visit Washington, DC.

They are quite common in some municipalities. There are folks who talk about this at length in cybersecurity circles every year at conferences, it’s been an issue for a long while and the scope of the problem continues to grow.

The EFF also writes in the topic from time to time. See: https://www.eff.org/deeplinks/2024/06/next-generation-cell-s...

Is it possible to detect these using SDR networks?

https://www.rtl-sdr.com/kiwisdr-tdoa-direction-finding-now-f...

I have no idea. I'm not an RF expert, but I'll ask this the next time I run into one. Great question!

Here in Brazil criminals are starting to use those to send phishing SMS, exploiting our ubiquitous mobile payment system (pix) or pretending to be a second authentication factor for banks.

I can see why they'd write it for a specific cheap device. Is this stuff possible with a typical phone modem, though; or does it rely on some special features? Forgive my ignorance. :)

Possible, yes, it's just looking at various 3GPP network messages and parsing out a few common anomalies. Accessible, not all the time.

This project uses QMDL (Qualcomm debug logging) on a device with an accessible modem debug port and debug logging enabled. Most older Qualcomm devices have this form of debug logging available by default, but on newer devices, the debug interface is usually more locked down, requiring some degree of shenanigans to access.

Take a look at SnoopSnitch (similar project for Qualcomm Android phones), QCSuper and MobileInsight (tools capable of capturing signaling data from QC and Mediatek phones), and SCAT (capable of capturing signaling data from some Samsung basebands).

Other vendors usually have similar debug modes for their modems, but they often aren't reverse engineered or as easy to access as the Qualcomm ones.

Amazing reply, thank you!

In the blog post[0], they mention it being possible with rooted Androids - so likely possible, just requires more access to what the modem's doing than the OS normally provides. [0]: https://www.eff.org/deeplinks/2025/03/meet-rayhunter-new-ope...

I see the devices vary quite a bit in price on eBay: Verizon, Unlocked, etc. Anyone know if it matters whether locked, Verizon, AT&T, etc.?

You can buy these off eBay for pretty cheap.

Unlocked RC400L's are going for ~$19.99

Gunna look into getting one and making one of these to play with.

Blog post: https://news.ycombinator.com/item?id=43258620

iPhone Field Test Mode can be informative, https://www.xda-developers.com/how-access-field-test-mode-io... when combined with open data on cell tower identity, https://opencellid.org

  Dial *3001#12345#*

It can sometimes be informative to turn off Data Roaming in cellular settings.

(e)SIM password can provide an additional layer of control over when the phone contacts a cellular tower.

Wow! Thanks for the information! Very neat!

What's inside the Orbic? Any chance to make this work on a different device. Orbics don't seem to be very easy to get in Europe.