It's an unfortunate truth that weapons and explosives in public places are an increasing problem, with some schools in the US beginning to implement security checkpoints. But many of these technologies are bulky and expensive to set up, and require staff to operate. Now a new study has found a way to tap into a type of signal that's already ubiquitous in many public places – plain old Wi-Fi.

Currently, detecting suspicious objects in bags and backpacks can require dedicated and costly equipment like surveillance cameras, X-ray machines and ultra-wide-band scanners. Sometimes bag checks are done manually, but this requires staff to be present and can invade the privacy of people passing through.

The goal of the new study was to simplify the detection of weapons, bombs, and dangerous chemicals using more readily available technology. Involving scientists from Rutgers University New Brunswick, Indiana University–Purdue University Indianapolis and Binghamton University, the project investigated using Wi-Fi, which is already widely installed in many public places.

Wi-Fi works off radio frequency signals, and conveniently reacts to bags made of fiber or plastics much differently than it does to metals or containers of liquids which could constitute dangerous objects. It even has the capacity to estimate the volume of liquids present, including water, acids, alcohols and other chemicals that may be used for explosives.

To explore these possibilities, the team set up a system with two or three Wi-Fi antennas and scanned 15 types of objects hidden inside six types of bags. Through a series of experiments, the technology was found to have a detection accuracy of 99 percent for dangerous objects, 98 percent for metals, and 95 percent for liquids. In a normal backpack, the accuracy rate was usually over 95 percent, and even when objects were wrapped up it still hit around 90 percent.

As it stands, this method does still require that people pass through a security checkpoint, and staff will be needed to conduct the scans. But the team says the value of using Wi-Fi is the low cost, since the system can be easily integrated into existing networks.

"This could have a great impact in protecting the public from dangerous objects," says Yingying Chen, co-author of the study. "In large public areas, it's hard to set up expensive screening infrastructure like what's in airports. Manpower is always needed to check bags and we wanted to develop a complementary method to try to reduce manpower."

In future work, the team plans to hone the system to make it more accurate at identifying objects by imaging their shapes, and estimating the volumes of liquids.

The research was presented at the IEEE Conference on Communications and Network Security (PDF).

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