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Geofencing strikes again. Last week, CNBC reported on an accused bank robber who was apprehended by authorities in Virginia after police issued a warrant for Google location data from cellphones in operation near the scene of the crime.

Meanwhile, the suspect's legal team is mounting a Fourth Amendment defense, arguing that the methods the police used to track down the alleged robber was akin to "searching every home in the neighborhood of a reported burglary."

Since geofencing shows no signs of slipping out of favor with law enforcement any time soon, courts will likely continue to butt up against arguments related to illegal search or seizures. However, making changes to the way police have traditionally gone about leveraging that tool could have big repercussions for how the government conducts investigations as a whole.

"There's no solution to this yet," said Rich Goldberg, a partner at Lewis Brisbois Bisgaard & Smith.

Right now, the typical procedure a law enforcement agency might undertake in order to obtain a warrant for geofencing-related data varies from judicial district to judicial district.

Jarno Vanto, a partner at Crowell & Moring, said that while some jurisdictions may utilize a single warrant approach, others are more deliberate in an attempt to filter the amount of personal information they collect that is ultimately irrelevant to the case at hand.

For example, police might first request a warrant for a pool of non-identifiable devices. Once that list of devices has been suitably narrowed down, they would return to the phone or communications company with a second warrant for more identifiable information.

Not all companies are eager to comply, given the potential for backlash from privacy-wary consumers. According to NBC News, Google has previously fought law enforcement attempts to obtain location data absent a warrant. "Phone companies are actually actively battling these requests. They are challenging these warrants," Vanto said.

But tech and phone companies aren't the only ones, as evidenced by the Fourth Amendment-centric argument mounted by the defense team in the Virginia bank robbery case. This is where establishing the probable cause behind the warrant becomes essential.

"Whether there's probable cause for a search really comes down to, can [a suspect] be identified based on that search?" Vanto said.

Still, the use of phone records in an investigation is not all that unusual, even if the scope and location-based nature of geofencing does present a few new wrinkles. For example, the 1979 Supreme Court case of Smith v. Maryland determined that a pen register—a device that records all numbers dialed on a phone line—was not a search because the "numerical information" was being voluntarily conveyed to the phone company.

Per Goldberg, the case established that information customers provide to institutions they do business with, such as telephone companies or a bank, can be obtained by the government without a warrant.

Of course geofencing embellishes on the scenario presented in Smith v. Maryland by introducing the ability to track someone's location using their phone. A June 2018 decision rendered by the Supreme Court in the case of Carpenter v. United States addressed that development, stating that the government could not access historical cell phone data without a warrant.

However, the ruling also took pains not to undercut Smith v. Maryland too severely, stressing that the same restrictions did not apply to banking records or cell tower data collected in an emergency or for national security issues.

"If they were to change [Smith v. Maryland], they would change the way all government investigations are done. It would essentially make it really difficult to gather bank records. Really simple things—the records that businesses keep," Goldberg said.

But if law enforcement continues to make geofencing a part of its toolbox, it seems likely that courts will continue to field Fourth Amendment concerns. However, arriving on a general rule that can span multiple jurisdictions may continue to be a challenge.

A big part of that may come down to the difference between requesting location data for all of the cell phones within a four-block radius of rural Virginia and then attempting the same in downtown Manhattan. The amount of information being caught in the net varies greatly.

And then there's the speed of technological development.

"[The court] is very reluctant to set up rules that say, 'OK, the government can do this, it can't do that.' Because they know technology will make that opinion look stupid," Goldberg said.