Cell phone location tracking is no longer just the domain of emergency services and shadowy government investigations. New research from a group of scientists at Northeastern University in Boston say they've practically struck gold with cell phones, using their location-tracking features to draw conclusions about 100,000 subscribers to an undisclosed European cell provider.

The study, titled "Understanding Individual Human Mobility Patterns" and published in the latest edition of the journal Nature, sought to figure out where people go throughout their day. Scientists have previously struggled with the task, as tracking something as "ephemeral" as peoples' movements in a reliable, non-intrusive method proves to be highly difficult. Cell phones and the location-tracking data that telcos collect on them as people move near different towers, seems to have bridged this gap. People are generally never far from their phones, and their location-tracking traits are completely passive so much that many people aren't even aware they are being tracked.

"Slices of our behavior are preserved in these electronic data sets," said project director Albert-László Barabási. "This is creating huge opportunities for science."

Privacy groups are not sitting easy with the study's methods, however. Marc Rotenberg, president and founder of the Electronic Privacy Information Center in Washington D.C., called the study "troubling," noting that it "raises questions about the protection of privacy in physical spaces, when devices make possible the capture of locational data."

Ethically, the study exists in a gray area as well. The study's "participants" -- the 100,000 subscribers of the undisclosed European country -- were not informed of their participation. While scientists are generally allowed to observe people in public areas, examining location-tracking data is a new development in the research world and has yet to be classified one way or another.

The researchers say that they received dataset with personal information scrambled out, from a telephone company that was obligated to collect location-tracking information for other reasons. Further, they say their data is only as precise as the nearest cell tower -- and that it only shows information from when someone uses cell service, like sending a text message or receiving a phone call.

Despite their privacy precautions, however, the researchers acknowledge that most people's movements are so predictable that they can reasonably forecast the likelihood of someone being in a particular spot, regardless of how obfuscated their phone number is.

"Individuals display significant regularity, because they return to a few highly frequented locations, such as home or work," reads the paper.

While peoples' propensity for going to and from the same locations seems like an obvious conclusion, similar research has been confined to methods far less accurate. A previous paper, written by a physics professor Dirk Brockmann at Northwestern University, tracked people using data from dollar-tracking site wheresgeorge.com. It too reached a similar conclusion regarding people's lack of variation, but Brockmann's research was limited because, unlike cell phones, currency is rapidly passed around.

"Dollar bills diffuse, but humans do not," noted the Northeastern study.

The article in Nature notes that good data on human movements is useful to a number of fields. Urban planners can better allocate projects and resources to where people actually go, and epidemiologists can better track the spread of viruses and other threats.

"This is a new step for science," said Barabási. "For the first time we have a chance to really objectively follow certain aspects of human behavior."