WiFi Signals Can Detect Concealed Handguns, Swedish Study Shows

WiFi signals can be used to detect concealed handguns and alert security, according to a study by the Swedish Defense Research Agency (FOI). The researchers demonstrated a prototype that located up to 90% of the items carried by up to 4 people walking in a room.

How the system works

The experiment setup was quite rudimentary. Researchers placed 2 WiFi transmitters on one side of the room and 2 receivers on the other. An operating frequency of 5.68 GHz was used, the same as on many home routers, with a bandwidth of 20 MHz, the narrowest standard WiFi channel. Data was collected using a modified open-source implementation of IEEE 802.11a, an older WiFi standard from 1999, and GNU Radio, free software for radio signal processing.

Up to 4 participants walked in the up to 12-square-meter area covered by WiFi signals, while a standard video camera filmed everyone. The core idea is that WiFi signals are distorted differently as they pass through people and objects, such as a metal handgun, a water bottle, a phone, or a plastic toy gun.

The researchers utilized WiFi Channel State Information (CSI), a detailed measurement of how radio waves propagate, reflect, and change. CSI slices the 20 MHz channel into 52 narrow frequency segments and measures amplitude and phase 80 times per second. The deep learning model, called WiFireNet, learned to recognize handgun patterns and draw a 2D box around the person it thinks is carrying a gun. It was trained to distinguish 4 common classes: a handgun, a plastic handgun, a metal water bottle, and a mobile phone.

Results and limitations

According to the results, the system found 83% to 91.5% of objects people carried, depending on room size and number of people. However, it also makes many mistakes. The mean average precision score, which punishes false positives, was around 35% to 50%. The average precision for the handgun class alone ranges from about 30% to 72%.

The authors argue that CSI signals cover a wide area, can spot hidden items, and do not need a security gate with a guard. "A WiFi-based security system has the potential to be a complementary modality that is able to handle occlusions or concealment and is not hindered by strict spatial configurations," the researchers explain.

Open release

The collected data, code, and trained model are now public for other labs to reproduce or improve. The researchers note that WiFi signals are already being used to detect intruders, sense presence, or even see through walls, and claim that no prior work has been done on WiFi-based handgun detection in dynamic multi-person environments.

Sources: Cybernews