The next time you drive past one of those road signs with a digital readout showing how fast you’re going, don’t simply assume it’s there to remind you not to speed. It may actually be capturing your license plate data.

According to recently released US federal contracting data, the Drug Enforcement Administration will be expanding the footprint of its nationwide surveillance network with the purchase of “multiple” trailer-mounted speed displays “to be retrofitted as mobile LPR [License Plate Reader] platforms.” The DEA is buying them from RU2 Systems Inc., a private Mesa, Arizona company. How much it’s spending on the signs has been redacted.

Two other, apparently related contracts, show that the DEA has hired a small machine shop in California, and another in Virginia, to conceal the readers within the signs. An RU2 representative said the company providing the LPR devices themselves is a Canadian firm called Genetec.

The DEA launched its National License Plate Reader Program in 2008; it was publicly revealed for the first time during a congressional hearing four years after that. The DEA’s most recent budget describes the program as “a federation of independent federal, state, local, and tribal law enforcement license plate readers linked into a cooperative system, designed to enhance the ability of law enforcement agencies to interdict drug traffickers, money launderers or other criminal activities on high drug and money trafficking corridors and other public roadways throughout the U.S.,” primarily along the southwest border region, and the country’s northeast and southeast corridors.

“There used to be an old police saying, ‘If you robbed a bank, please drive carefully,’” former NYPD Detective Sergeant and Bronx Cold Case Squad commander Joseph Giacalone told Quartz, explaining that if a getaway driver didn’t do anything to attract the attention of police and get pulled over, they usually had a half-decent chance of fleeing. “But that’s no longer in effect because you can drive slow, you can stop at every red light, but these license plate readers and surveillance cameras track your every movement.”

And therein lies the real issue: What is a game-changing crime-fighting tool to some, is a privacy overreach of near-existential proportion to others. License plate readers, which can capture somewhere in the neighborhood of 2,000 plates a minute, cast an astonishingly wide net that has made it far easier for cops to catch serious criminals. On the other hand, the indiscriminate nature of the real-time collection, along with the fact that it is then stored by authorities for later data mining is highly alarming to privacy advocates.

“License plate readers are inherently a form of mass surveillance,” investigative researcher Dave Maass of the nonprofit Electronic Frontier Foundation told Quartz. “You look at something like a wiretap and most of the time it’s looking for a specific person and capturing specific conversations with that person. But here they are collecting information on everybody, not all of whom have been accused of a crime, in case they may one day commit a crime. This is un-American.”

The DEA does not release how much of the data it collects is connected to crimes. The nonprofit American Civil Liberties Union of Maryland found that only 47 out of every 1 million plates scanned by police in the state, or 0.005%, were linked to a serious crime. The Atlanta PD captured data from 128.5 million license plates last year; 786,580 of those—0.6%—were suspected of having a connection to a crime. Of 22 million license plates recorded in Austin, Texas during that same period, 3,200 of them—0.01%—were linked to alleged criminal activity.

Still, it’s not the data collection itself that’s the issue, as much as what authorities do next with that information, explained Maass.

“The technology is fairly simple, but as they start collecting more and more data and applying more and more algorithms to that, you can get information about people’s travel patterns, where their doctor’s office is, where they sleep at night, or put in the address of a place and see who visited it: an immigrant health clinic, a medical marijuana facility, or even a [marijuana] grow [operation] that would be completely legal under state law but illegal under federal law,” Maass said. “You could [link someone to] an abortion clinic, any number of sensitive locations.”

Precise details of the DEA’s license plate reader program are extremely difficult to pry loose. The DEA declined to comment on either the program in general or its latest purchase of license plate readers; Sherman Green, the Department of Justice contracting officer handling the RU2 deal did not respond to an interview request.

Maass said the DEA augments its own data collection by buying access to commercial databases, including one maintained by Vigilant Solutions of Livermore, California. In January, the US Immigration and Customs Enforcement agency purchased access to Vigilant’s LPR data which reportedly allows investigators to trace plates going back five years.

Some LPR cameras can capture “contextual photos,” which include shots of the driver and passengers. Companies like Palantir Technologies, which was co-founded by controversial venture capitalist Peter Thiel in 2003, make analytics software that can combine license plate data with all manner of other intelligence, including facial recognition technology; officers can access Vigilant’s “Intelligence-Led Policing Package” on their mobile phones.

Law professor Andrew Ferguson, a former public defender and author of 2017’s The Rise of Big Data Policing: Surveillance, Race, and the Future of Law Enforcement, said the DEA “finds itself at the intersection of new technology scandals [accusations of secret, and possibly illegal, bulk data collection by the DEA have surfaced in recent years] because they maintain both domestic and international jurisdiction and thus can argue the need to use surveillance tools that would not be acceptable in purely local law enforcement.”

“For example, most other domestic law enforcement agencies couldn’t claim any right to know information from secret NSA wiretaps…but because the DEA can claim that they are tracking international drug traffickers and thus need to know information obtained outside the states, they can use invasive techniques domestically.” In addition, the DEA has largely worked under the radar, as our national approach to large scale drug prosecutions has not changed from administration to administration. The DEA has been funded, and with federal funds comes playing around with new surveillance technologies.”

Jay Stanley, a senior policy analyst with the ACLU’s Speech, Privacy, and Technology Project, told Quartz he thinks it’s wrong for the government to arbitrarily collect such a broad swath of data in the first place. Holding onto it for future analysis only makes things worse, he said.

However, the law enforcement community at large argues that none of this data is being used to spy on everyday Americans.

“We don’t know when somebody’s going to commit a crime, we don’t know when somebody’s going to run over somebody and take off,” said Joe Giacalone. “So that data should be there forever. We never know when we’re going to need it.”

Kabrina Chang, a professor of law and ethics at Boston University’s Questrom School of Business told Quartz, “We as a society have to think long and hard about the consequences. I don’t think anyone would begrudge law enforcement help in doing their jobs; we all want them to do their jobs really, really well. But what are we willing to give up?”

DEA expects to take delivery of its new license plate-reading speed signs by October 15.