The public transit system in Los Angeles has announced that it is the first in the U.S. to purchase millimeter wave scanners to screen metro riders for suspicious objects as they move through stations, NPR reports.

The technology “will help detect weapon and explosive device security threats on the county’s transit system,” the system says in a joint press release with the TSA on Tuesday.

The LA metro ordered several units at approximately $100,000 each, and the portable body scanners use similar technology to the devices installed in airports to look for metal and nonmetal objects concealed in clothing. Unlike airports’ scanners, these devices detect radiation released by riders’ bodies, and the “Thruvision” devices monitor people as they walk through the station like normal instead of needing passengers to line up and pass through the system one by one, according to the NPR article. 

The Los Angeles County Metropolitan Transportation Authority’s rail system is the ninth-largest metro in the U.S., and more people ride the system’s trains on an average weekday than fly through Los Angeles International Airport. Because the devices are portable, they can be moved between stations, either at random or to respond to specific concerns. Signage will warn LA Metro riders that they are approaching an area where they are subject to screening.