SDR (Signals Intelligence) for Hackers: Scanning Wireless Devices Using FieldWatch

What it is

FieldWatch is a free, open-source Android app that passively scans Wi-Fi and Bluetooth with the phone's own radios and matches what it hears against an editable catalog of about 250 device signatures. It only receives and never transmits. Everything runs on the device and works offline.

Preconditions / Affected

• Android 10 or newer is required. Android 11 unlocks more functions, though the page doesn't say which.
• A cheap phone with no SIM is enough. The author cites a report of a $30 Moto G working well. The page also advises newer phones for better results.
• Results are limited by what the phone's radios and Android expose to the app.

What to do

• Sideload the APK from the official GitHub repo. The page says official versions come only from there. A short instruction file and manual ship with it.
• Set alerts for specific devices, and record sessions on a walk or drive so you can compare them later.
• For GNSS spoofing or jamming checks, use a newer version and do a short outdoor calibration first. Alerts are then marked on your path or on a TAK map.
• For team use, TAK/ATAK export goes over the local network. Several phones can feed one shared map. A Remote ID drone appears as a moving marker, with a second marker for the pilot if that location is available.

flowchart LR
    A[Phone Wi-Fi + BT radios] --> B[Signature match]
    B --> C[Alerts / sessions / path map]
    B --> D[TAK over local network]
    G[Phone GNSS receiver] --> E[Interference check after calibration]
    E --> C
    E --> D

Caveats

• Matches are pattern-based, not confirmed identities.
• It is not a direction finder. GNSS alerts show where you were when interference occurred, not where it came from.
• It does not scan Bluetooth Classic, cellular, or full Wi-Fi traffic.
• The page is an overview from a training vendor and gives no detection-accuracy figures. The Moto G result is a secondhand social media report, not a benchmark.