Legally Track Smartphone Users via an ESP8266 Microcontroller
Amine Mehdi Mansouri's device is small enough to fit it in hidden places like books, shelves, or his pocket.
What started as a project for checking the connection status of his IoT plant sensors, engineering student Amine Mehdi Mansouri found (after doing some research) that people were using the probe requests sent by mobile devices to announce the SSIDs they connected with. Smartphones, laptops, and other gadgets routinely check for Wi-Fi connections, and most of them save previously connected network information, which is shared with anything that's actively listening. Those public packets essentially show where the user has been, as well as the device's unique MAC address.
Mansouri designed a device based on the ESP8266 that could grab that information and be used to track people who were in range of the board. "The board has roughly 12 components onboard, all of them surface mount and easy to solder with an 0805 package," states Mansouri. "It has a green led to indicate when it's on and a reset button in case I want to update Wi-Fi creds (SSID and pass)."
To get the device to track individuals properly, he needed to create a mesh-like network using eight boards, along with a series of Kortex Xtend Lite NAT (Wi-Fi) repeaters. Mansouri then tested his tracking platform at his local library (with permission), where he set up eight boards in different places that experienced a lot of traffic. The repeaters were used to see who connected to the library's Wi-Fi, while the MAC sniffing devices collected the addresses from the mobile devices.
With his simple deployment, Mansouri managed to target 526 MAC addresses over two days, each with their RSSI values, denoting the proximity of each person to the nearest device. It's an exciting project, to say the least, and for those interested, Mansouri has uploaded a detailed walkthrough of his build on his project page.