Chasing Your Tail - Wi-Fi / Bluetooth Follower Detector

Watches for the same phone or earbuds turning up behind you twice.

Placeholder illustration. Real photographs go here once we have finished hardware to photograph — we will not use stock images of somebody else's equipment.

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A Raspberry Pi with a monitor-mode Wi-Fi adapter and a touch screen, running the Chasing Your Tail NG tool on top of Kismet. It listens for the radio signatures of nearby devices and alerts when one it saw a while ago shows up again somewhere else. That repeat is the pattern that says you are being followed rather than passed.

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MIT (application) on GPL-2.0-or-later (capture engine) — source code ships with the unit.

// CAPABILITY

What it does

Passively listens for Wi-Fi and Bluetooth devices nearby - phones, earbuds, headsets, trackers - using Kismet as the capture engine.
Compares what it sees now against rolling 5, 10, 15 and 20 minute windows and alerts when the same device signature reappears later, in a different place.
Runs standalone on the official Raspberry Pi touch display, so you can work a route from a vehicle with no laptop and no phone involved.
With the optional USB GPS attached, logs where a repeat device was seen and writes a session report plus a KML track you can open in Google Earth.
Builds an ignore list of your own gear first - your phone, your earbuds, your truck - so it stops alerting on you.
Works with no internet connection at all. It is assembled and installed fully offline, and there is no cloud account anywhere in the product.

// LIMITATIONS

What it does NOT do

Read this part. It is the half of the specification most sellers leave out.

It does not identify people. It sees radio device signatures, not names, faces, or plates.
It cannot detect anyone following you who has no Wi-Fi or Bluetooth device powered on, has everything in airplane mode, or is in a vehicle broadcasting nothing.
A repeat hit is a candidate, not proof. Shared commutes, neighbours, delivery routes and the same truck leaving the same holler at the same time every morning all produce honest repeats.
Without the GPS option there is no location logging. You get "seen again", not "seen again here".
MAC address randomisation on modern phones means some devices will simply be missed. The tool is built around repetition over time precisely because fixed addresses cannot be relied on, but that is a mitigation, not a cure.
The WiGLE lookup feature - guessing where a device is usually based - needs an internet connection and a free API key. It is optional and off by default. Core detection never touches the network.
If you skip building the ignore list, it will alert on your own equipment all session.
It does not jam, block, or interfere with anything. It only listens.

// HARDWARE

Specifications

Computer

Raspberry Pi 4, 8 GB preferred, Raspberry Pi OS Bookworm 64-bit

Sensor

USB Wi-Fi adapter with monitor-mode support (Alfa class). Monitor mode is required; packet injection is not used

Storage

High-endurance microSD, 32 GB or larger - this logs continuously and a cheap card will not survive it

Display

Official Raspberry Pi Touch Display, 800x480, for standalone operation

Capture engine

Kismet 2025-09-R1, compiled on the device

Detection logic

Device-signature recurrence across rolling 5 / 10 / 15 / 20 minute windows

Options

VK-162 USB GPS for route logging and KML export; USB power bank for untethered field use

Outputs

Session report (Markdown/HTML) and, with GPS fitted, a KML track

Network

No internet required for detection, reporting, or mapping

// OPEN SOURCE

Licence & attribution

MIT (application) on GPL-2.0-or-later (capture engine)

The detection application is Chasing Your Tail NG, copyright Argelius Labs / @matt0177, MIT licensed - its licence and copyright notice stay on the device. The capture engine is Kismet, copyright the Kismet authors, licensed GPL-2.0-or-later. The complete corresponding source for the exact Kismet build on your unit is written onto the device itself at /usr/local/share/kismet-source, and we will also supply it on written request for three years after sale.

// FREQUENT QUERIES

Straight Answers

Does it work from a vehicle?

That is its main use. Pi, touch display, and either vehicle USB or a power bank. Drive your route and watch the window alerts. With GPS fitted you get a track afterwards showing where each repeat happened.

Modern phones randomise their addresses. Doesn't that defeat it?

Partly, and we will not pretend otherwise. The tool was deliberately built around temporal recurrence rather than a fixed hardware address, which is what makes it work at all against randomisation. It still means some devices will be missed.

Does it phone home or need a subscription?

No. Detection, reporting and mapping are entirely local. The only feature that touches the internet is an optional WiGLE database lookup, which needs a free API key and is off unless you ask for it.

Can it tell me who is following me?

No. It tells you that a device signature repeated, when, and - with GPS - where. Who that device belongs to is a question for a deputy or an investigator, with your session report in hand.

Who wrote the software?

Matt Edmondson of Argelius Labs, a federal agent of twenty-two years, originally to help protect confidential informants. It was presented at Black Hat Arsenal and has since been used for search-and-rescue and for emergency-room staff safety. It is a real tool with a real history, not a weekend project.

// NEXT ACTION

Talk to us before you buy a detector

Tell us what you are actually worried about. Half the time the honest answer is a different device, or none of them.

Request a Site Assessment Call (304) 555-0142