The nation’s mobile phone carriers received more than 9,000 requests last year for cell-tower dumps, which identify every mobile phone at a particular location and time, often by the thousands.

The revelation, revealed in a congressional inquiry, underscores that domestic authorities, from the FBI to the local police, are performing a massive amount of surveillance on Americans on domestic soil, sometimes without probable-cause warrants.

Figures provided by the nation’s largest carriers, T-Mobile, Sprint, Verizon and AT&T, and smaller companies, like C-Spire and Cricket, show that the carriers overall got as many as 1.1 million requests for customer cellular data last year. They’ve earned tens of millions of dollars processing the data, the records show.

The governments requests, most of which were honored, include data for, among other things, the geo-location of a device, call detail records, texts message contents, voicemail, cell tower dumps, wiretapping, subscriber information, and websites visited.

But the most startling figures show that the authorities are obtaining information on the whereabouts of perhaps thousands of people at once, often by a judge's signature based on assurances from the authorities that the data is relevant to an investigation.

A myriad of factors determine how many people are caught in the web of one of these so-called "cell-tower dumps" or "searches," including the time, location and a mobile-phone tower’s capacity. The data from a dump can provide a wealth of information regarding whoever is carrying a mobile phone in a tower’s area — from the phone number to various device information pointed to a phone’s account.

According to Verizon: (.pdf)

Although we do not specifically track the details of each tower request, our experience is that we typically receive requests for less than 30 minutes (e.g., where law enforcement is already able to pinpoint the time of a crime). But we also receive requests covering more than an hour (e.g., where there has been a crime spree). When we receive a demand for a longer period, cognizant that the cell tower dump will contain many mobile device numbers, we will often ask law enforcement to narrow the scope of the time period or accept reports run for shorter, incremental periods, even if the longer time period was approved by a judge. The number of mobile device numbers per cell tower dump depends on many factors including the location of the tower and the time day. A major event (like the Boston Marathon) may lead to a substantial increase in the number of mobile device numbers communicating with a tower at a given time.

Sprint said it "provided approximately 6,000 cell tower searches (.pdf) to law enforcement agencies." T-Mobile did not answer the question.

The responses were released today as part of an inquiry by Sen. Edward Markey (D-Massachusetts).

"As law enforcement uses new technology to protect the public from harm, we also must protect the information of innocent Americans from misuse, said Markey, who is a member of the Commerce, Science and Transportation Committee. “We need a Fourth amendment for the 21st century. Disclosure of personal information from wireless devices raises significant legal and privacy concerns, particularly for innocent consumers. That is why I plan to introduce legislation so that Americans can have confidence that their information is protected and standards are in place for the retention and disposal of this sensitive data."

The disclosures come amid revelations from NSA whistleblower Edward Snowden that National Security Agency snoops are harvesting as many as 5 billion records daily, without warrants, to track mobile phones as they ping nearby cell towers across the globe.

The law on cell-site locational tracking — while generally favorable to the government — is far from clear. Courts are offering mixed rulings on whether warrants are needed, and the Supreme Court has yet to take a case to resolve the issue.

Markey’s proposed legislation, which he is expected to drop within the coming weeks, would require probable-cause warrants for mobile-phone location tracking "to believe it will uncover evidence of a crime. This is the traditional standard for police to search individual homes."

Chris Calabrese, the legislative counsel for the American Civil Liberties Union, said: "The idea that police can obtain such a rich treasure trove of data about any one of us without appropriate judicial oversight should send shivers down our spines. There is an easy fix to part of this problem – President Obama and members of Congress should pass legislation that updates our outdated privacy laws by requiring law enforcement to get a probable cause warrant before service providers disclose the contents of our electronic communications to the government. Anything less is unnecessarily invasive and un-American."

The figures, meanwhile, although they show that the carriers are all over the map in terms of whether warrants are required for dumps, also reveal that the carriers keep the data for differing time periods, too. For example, U.S. Cellular and Verizon keeps cell-tower data for a year. T-Mobile (.pdf) and Sprint retain it for 180 days and AT&T five years. Markey would like to see a nationwide, uniform approach to that.

AT&T said the average cell-tower dump was 80 minutes. (.pdf) The company said it charged $10.3 million last year furnishing thousands of request for data to the authorities last year. Verizon, which reported 2,400 tower dumps, said it charged "less than" $5 million last year to comply with all government demands for customer and cell-site monitoring.