Chasing your Tail with a Raspberry Pi

The talk starts with a request from a contact who worried that he was being followed after meeting a confidential informant, and who wanted a way to check for that. The speaker explains why the idea seemed worth building, and also weighs whether the design could be misused for stalking. He concludes that it was built only to flag repeat followers and that the approach is useful to share.

The core of the build is a passive monitor. A Raspberry Pi runs Kismet with an external Wi-Fi adapter, a Bluetooth adapter, a battery pack and a small touch screen, logging nearby devices to a database without connecting to them. A Python script compares devices seen in the last minute against rolling lists from the previous 5 to 20 minutes and raises an alert when one reappears. Field testing showed that many phones randomize their MAC addresses, so the script also tracks the network names each device probes for. An ignore list lets the user exclude devices already around them before a drive.

The speaker closes with a live demonstration and a list of next steps, including more radios, GPS logging, tire pressure sensors and AirTag-style detection. The code was released on GitHub. The main takeaway is that cheap, passive monitoring can support counter-surveillance, but it needs comfort with Linux and careful interpretation of what the data shows.