Ordinary wi-fi could be used to detect weapons and explosives in public places, according to a study led by the Rutgers University in New Jersey.
Wireless signals can penetrate bags to measure the dimensions of metal objects or estimate the volume of liquids, researchers claim.
Initial tests appeared to show that the system was at least 95% accurate.
It could provide a low-cost alternative to airport-style security, researchers said.
The team behind the research tested 15 types of objects and six types of bags.
The wi-fi system had success rates of 99% for recognising dangerous objects, 98% for metal and 95% for liquids.
When objects were wrapped inside bags, the accuracy rate dropped to about 90%.
The low-cost system requires a wi-fi device with two or three antennas and can be integrated into existing wi-fi networks.
The system works by analysing what happens when wireless signals penetrate and bounce off objects and materials.
It could be utilised in museums, stadiums, theme parks and schools or wherever there is a perceived public risk.
"In large public areas, it's hard to set up expensive screening infrastructure like what is in airports," said Yingying Chen, co-author and a professor in the Department of Electrical and Computer Engineering in Rutgers-New Brunswick School of Engineering.
"Manpower is always needed to check bags and we wanted to develop a complementary method to try to reduce manpower."
She added: This could have a great impact in protecting the public from dangerous objects. There's a growing need for that now."
The peer-reviewed study received a best paper award at the 2018 IEEE Conference on Communications and Network Security on cyber-security.
It included engineers at Indiana University-Purdue University Indianapolis (IUPUI) and Binghamton University.