This DIY device can tell you if you’re being followed on the street

A cybersecurity specialist has created a device that can detect nearby smartphones, tablets and connected objects. Its system is based on consumer components, which many geeks may already have at home.

How do you know if someone is following you? This question was put to Matt Edmondson, a federal agent who works for the United States Department of Homeland Security (DHS). The request was made by a friend who also works for the government and had fear of being followed by meeting an informant with ties to a terrorist organization.

He presented his solution during the conference Black Hat USA this month. For less than 200 euros, he created a device capable of scanning the frequencies Bluetooth, WirelessSDR, ZigBee, etc. and locate nearby devices. He uses a minicomputer raspberry-pipowered by an external USB battery (like those for the smartphones). He added a little touchscreen, and finally a USB Wi-Fi module. the raspberry-pi already integrates Wi-Fi. However, it does not support the mode monitor which allows all traffic from the wireless network to be received.

Consumer equipment

His system uses software Kismet to analyze wireless communications. He started by recording the MAC address of devices, but soon realized that many could change it randomly with each connection attempt. It is therefore associated with the name (SSID) of the network sought by the devices. Every five minutes, his system creates a new file in which it saves information from all nearby devices. If the same device is present in multiple files, i.e. has been detected nearby at least five minutes apart, it receives an alert.

Reproducing his system, which he baptized ” chasing your tail “, is within the reach of all those who have a little experience with the systems linux. He used mainstream components and published his code on GitHub. He hopes to improve his system by adding other protocols wireless, as well as a GPS to be able to record the location of the devices.