Dec 11, 2014 · 1 minute

Sen. Jon Tester (D-MT) has sent a letter to the Department of Homeland Security and outgoing Attorney General Eric Holder to learn more about the use of "dirtboxes," which collect phone data by masquerading as a nearby cell tower. The letter, which was co-signed by Democratic and Independent senators from Alaska, Vermont, and other states, argues that dirtboxes "potentially violate the Fourth Amendment and represent a significant intrusion into the private lives of thousands of Americans." .

The senators wrote the letter, which was sent on Wednesday, in response to a Wall Street Journal report about a US Marshals program that attaches these dirtboxes to planes flying across the United States. This reportedly allows law enforcement to collect information about "tens of thousands" of citizens under the planes' flight path. It's not clear how often these planes are flown.

But it is clear that the devices  can determine someone's location within a few meters, which could allow law enforcement to tell if that person is in a specific room inside a building, instead of merely knowing their general location. The devices are also thought to be able to snoop on phone calls, text messages, and other information transferred to affected cellphones.

Much about this program, and the dirtboxes in general, remains unknown to the general public. Their abilities are guessed at, the frequency with which they're used is unknown, and it's unclear how much information is gathered about un-targeted civilians who happen to be caught in the device's dragnet, or for how long that data is stored after it's "mistakenly" collected.

Tester and his co-signers want to learn the answers to those questions. The senator says in his announcement revealing the letter's existence that he also wishes to make those answers available to the public so they know what law enforcement agents are doing with these devices. "While we all want law enforcement agencies to use cutting-edge tools to catch criminals and protect our borders," he said, "Americans should not have to sacrifice their privacy rights in the process."

In other words: perhaps law enforcement shouldn't be able to use the failed "war on drugs" to keep a program that collects an unknown amount of information from an unknown number of innocent people an unknown number of times each year secret from both lawmakers and civilians.