US Marshals Service

The next time you use your cell phone in a crowd, the US Marshals may be listening in.

The way it works is through a specialized box affixed to an airplane flying overhead, according to a report from The Wall Street Journal. That box is designed to trick mobile phones into communicating with it, sending all sorts of information through the air and into the device. And innocent Americans are just as likely to have their information collected as anyone else.

The Justice Department, which houses the Marshals Service, did not immediately respond to a request for comment.

The program is just one of many US government surveillance programs that have been detailed in the past years. Most famously, the National Security Agency's surveillance efforts has been said to collect swaths of data on millions of Americans, according to documents leaked by whistleblower Edward Snowden.

In both cases, the programs are ostensibly designed to track suspects, though information about innocent Americans is said to have been caught up in the efforts. Politicians, advocacy groups and activists say the government may not have the legal right to collect the information in such a sweeping way. They also debate whether it even should.

"The US Marshals should explain how this program works and what kind of court authorization, if any, they're obtaining," said Hanni Fakhoury, a staff attorney with the Internet civil rights advocacy group Electronic Frontier Foundation.

The initiative has been in existence since 2007 and operates out of at least five metropolitan airports -- enough to cover most of the US, according to the report. A key function is that the box apparently discards information not related to a specific suspect. Another feature: It can pinpoint the location of a suspect to within nine feet.